All AQA A-level Chemistry topic questions

AQA A-level Chemistry · Topic 3.1

Physical chemistry questions

Practice questions covering physical chemistry from this specification. Every question below is the real AQA question as it is printed on the paper, with its mark scheme.

Questions to attempt

6 questions on Physical chemistry, each with its mark scheme and worked method. Reveal the answer when you have had a go.

3.1.1.1 · Fundamental particles
Q1
ORIGINAL
A particle contains 15 protons, 16 neutrons and 18 electrons. State its overall charge and identify which particles are in its nucleus.
[3 marks]
Total for this question: 3
3.1.1.2 · Mass number and isotopes
Q2
ORIGINAL
An element has two isotopes, $^{50}\mathrm{Q}$ with abundance $73.0\%$ and $^{52}\mathrm{Q}$ with abundance $27.0\%$ . Calculate the relative atomic mass of Q.
[3 marks]
Total for this question: 3
3.1.1.3 · Electron configuration
Q3
ORIGINAL
Define first ionisation energy and write an equation, including state symbols, for the first ionisation of magnesium.
[3 marks]
Total for this question: 3
3.1.2.1 · Relative atomic mass and relative molecular mass
Q4
ORIGINAL
Calculate the relative formula mass of $\mathrm{MgSO_4\cdot7H_2O}$ . Use $A_r$ : H $=1.0$ , O $=16.0$ , Mg $=24.3$ , S $=32.1$ .
[3 marks]
Total for this question: 3
3.1.2.2 · The mole and the Avogadro constant
Q5
ORIGINAL
A sample contains $0.0125\,\mathrm{mol}$ of oxygen molecules. Calculate the number of $\mathrm{O_2}$ molecules. Use $N_A=6.02\times10^{23}\,\mathrm{mol^{-1}}$ .
[2 marks]
Total for this question: 2
3.1.2.3 · The ideal gas equation
Q6
ORIGINAL
Calculate the volume occupied by $0.0350\,\mathrm{mol}$ of an ideal gas at $315\,\mathrm{K}$ and $105\,\mathrm{kPa}$ . Give the answer in $\mathrm{dm^3}$ . Take $R=8.31$ .
[4 marks]
Total for this question: 4

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Printable question pack — 3.1 Physical chemistryAll 394 questions across 40 specification points — 388 more than the 6 above — with the full mark scheme. Guest accessible · browser print.

3.1 Physical chemistry revision notes

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Real past-paper questions

123 questions shown as printed, 66 reference-only · newest series first

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AQA 7405 · June 2025 · Paper 1 · Q1 · 11 marks
11 marks
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Over half the students scored both marks in part 1; some students were unfamiliar with the correct formula of titanium (IV) chloride and were unable to write a balanced equation. Some students did not know the role of magnesium. Answers to part 2 were good; common errors included incorrect formulas. In part 3 many students knew that magnesium hydroxide was less soluble than sodium hydroxide; common errors included reference to the base strength without linking their ideas to solubility or comparing the reactivity of NaOH and Mg(OH)2 Fewer than half the students scored both marks in part 4; some students did not attempt an ionic equation and used NaOH as their reagent. The bromide was well known in part 5, but many students did not write an ionic equation or omitted the state symbols in their equation. The most common answer for the explanation of acidification was to remove carbonate ions. Occasionally, students answered in terms of false positive results but failed to mention the ions involved. Part 6 was well answered.
Text version
This question is about some Group 2 elements and their compounds.
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AQA 7405 · June 2025 · Paper 1 · Q2 · 8 marks
8 marks
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About 50% of the students gained both marks in part 1; some students lost the second mark for not giving a comparative response or by not referring to the attraction between the nucleus and the outermost electron. Part 2 was well answered by the majority of students. In part 3, about one third of students correctly identified magnesium; argon, aluminium or silicon were common incorrect answers. Phosphorus was regularly identified in part 4 and most students recognised the jump in ionisation energy from 5 → 6; many students did not explain that a jump in the ionisation energy meant that an electron was being removed from an inner energy level. About half the © 2025 AQA students scored the mark in part 5; common incorrect answers included log 3.5 = 0.54 and 3.16 × 10–4.
Text version
This question is about ionisation energies.
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AQA 7405 · June 2025 · Paper 1 · Q3 · 23 marks
23 marks
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Just over 60% of students answered part 1 correctly. In part 2 many students lost this mark by not identifying the electron pair/lone pair was donated from oxygen to copper. Many incorrect observations were seen in part 3. The students who started with CO32– usually gave a correct equation; ions with incorrect formula CO3– were common. In part 4 most students gave the correct shapes; the most common error was square planar instead of tetrahedral. Some students did not refer to ligand size and instead gave ideas based on electron pair repulsion theory; some referred to chlorine atoms/molecules rather than chloride ions. Some students did not refer to d orbital splitting. Many students referred to light being absorbed but did not identify the light as visible or white. Many students knew that the colour seen was light that had not been absorbed. Few students were able to write about the energy gap and what was responsible for the change in the energy gap, although some did reference the equation ∆E = h𝜈𝜈. Fewer than 20% scored both marks in part 5. Many students gave an incorrect observation. Students found the equation challenging; chlorine was often given as a product, some students had 2 mol of ammonia and 4 mol of water instead of the other way round and the copper complex often lacked a charge. In part 6 many students could not give a balanced equation; H+ ions were often omitted from the left-hand side and water from the right-hand side. In part 7 most students gave the correct answer; a common error was to average three of the four titres instead of the two that were concordant. The calculation in part 7 proved challenging; most students were able to score the first three marks but then failed to divide by 2 and were not able to make progress. Some students used 25.0 cm3 for their titre. Students who had calculated an Mr greater than 275 usually divided this by 2 to get an Ar but often did not assign this to a metal with a +1 oxidation state. Students found part 9 challenging; common errors were to have a 4- coordinate copper or to bond the copper to a C2O42– ion via 1 coordinate bond. Many students did not specifically draw the coordinate bonds originating from the O atom of the water.
Text version
This question is about the chemistry of copper.
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AQA 7405 · June 2025 · Paper 1 · Q4 · 12 marks
12 marks
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About half the students answered part 1 correctly; many students lost the mark by adding extra incorrect information eg 1 mol dm–3 or all elements are in their standard states. Some students stated 1 atmosphere instead of 100 kPa. Many students could do the calculation in part 2; common errors included not applying the stoichiometry in the equation to calculate ΔH and ΔS and failing to use the factor of 1000 to calculate ΔS in kJ K–1mol–1. A few students could not rearrange the equation. Some students gave negative temperatures which are not appropriate in kelvin. In part 3 about 40% of students gained all the marks; many students made an error with the signs in the equation. © 2025 AQA The majority of students divided their final value by 8 and gained one mark although there were a few who divided by 4 and did not appreciate that there were two nitrogen to oxygen bonds in NO2. Answers to part 4 were generally good. In part 5 over half the students gained both marks. Some students stated that the equilibrium shifted in the endothermic direction without specifying this as being the reverse direction or without explaining that this was to oppose the change put on the system. It is advised to begin a response with a clear statement: eg the forward reaction is exothermic.
Text version
Nitrogen dioxide can be formed by heating magnesium nitrate and by reacting ammonia with oxygen.
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AQA 7405 · June 2025 · Paper 1 · Q5 · 10 marks
10 marks
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Many students failed to mention that van der Waals’ forces were between molecules in part 1; a few students referred to chloride and bromide ions. Some students confused the boiling point with ionisation energy and wrote about higher nuclear charge in bromine so stronger attraction between the outer electrons and the nucleus. A number of students thought that the covalent bonds break during a change of state and some students compared the reactivity of chlorine and bromine. Part 2 was generally well answered. Many students drew an acceptable diagram in part 3; a common wrong answer had three bonding pairs and one lone pair. The explanation proved more challenging; some students mentioned electron pairs repelling, but few qualified this with the electron pairs repel to be as far apart as possible. Part 4 differentiated well; observations were often incorrect eg white and cream precipitates, and HBr described as a brown gas. A correct equation for the acid -base equation was more successful than the redox equation. The redox equation was often unbalanced or contained incorrect formulas eg NaSO4 and BrSO4. In part 5 very few students gave an equation to form copper(I) iodide.
Text version
This question is about the halogens and some of their compounds.
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AQA 7405 · June 2025 · Paper 1 · Q6 · 9 marks
9 marks
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About one fifth of students gave correct equations in part 1; common errors included not balancing the half-equations with the species, or with electrons. In part 2, very few students explained that hydroxide ions were involved at both electrodes. A few students wrote that hydroxide ions were produced at the positive electrode but did not go further. Many students stated that the reactants were supplied continuously or that it was a reversible reaction. Many students could not answer part 3; some students scored a mark by stating that electrons were released at the negative electrode or by the hydrogen but often didn’t go on to explain that these flowed through the external circuit/motor to the other electrode. About one third of students gave the correct answer in part 4; common incorrect answers included N2 and SO2. In part 5, very few students linked storing hydrogen as a liquid to occupying less volume or minimising chance of escape. Part 6 was generally well done. In part 7, some students incorrectly stated that the half equations were the same; the correct idea that combining the two different sets of half equations, in both acidic and alkaline conditions, would lead to the same overall equation was not well understood. © 2025 AQA
Text version
An alkaline hydrogen-oxygen fuel cell uses two platinum electrodes in concentrated KOH(aq). Oxygen is supplied to one electrode and hydrogen to the other; the electrodes are joined through an external circuit containing a motor, and water leaves from the hydrogen side. The overall reaction is 2H2(g) + O2(g) -> 2H2O(l).
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AQA 7405 · June 2025 · Paper 1 · Q7 · 15 marks
15 marks
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Part 1 was well answered. In part 2 many students did not state that layers of atoms/ions can slide over each other; some students stated that metals were malleable or ductile or that vanadium was a metal. The equations in part 3 were generally well done; common errors included unbalanced equations with the correct species, or equations that had the wrong oxidation states for the vanadium oxides, many including positive ions e.g. VO+. In part 4, the majority of students did not recognize that the reduction of the vanadium species with tin proceeds in two steps and stops at V(III). A correct understanding of how EMF values determine the spontaneity of redox reactions was essential for full marks. Many students who did start and end with the correct vanadium species did not balance the equation. In part 5 many students clearly explained that the high melting point of ionic compounds is due to the strong electrostatic attraction between oppositely charged ions. Some students demonstrated confusion about the nature of the bonding; common errors included describing the bonding as molecular with van der Waals’ forces, macromolecular with covalent bonds, or metallic bonding. Few students were able to construct and balance the initial equation in part 6 to show the formation of the hexa-aqua complex; VO, VO2+ and H2SO4 were all common products. A common error was the misidentification of SO₄²⁻ as the acidic species, likely due to its association with sulfuric acid. However, in this context, sulfate is simply a spectator ion and does not contribute to acidity. In part 7 many students were confused by the instruction to use the symbol Q and instead attempted to write equations using the molecular formula. Many students used high energy electrons in their equation to knock an electron off the molecule and those who used the full formula did not add an H+ to the ion they formed or forgot to add the charge. Equations such as Q + H+ → QH and Q + H+ → Q+ were common. Few students gained M2, as many ignored the instruction to use a mass of 51 for vanadium. Instead, they used the relative atomic mass from the Periodic Table, which led to an incorrect calculated value of 601.9 rather than the expected result based on the given mass. More than 60% of students gained both marks in part 8. The students who found the question challenging could not give an expression linking the abundances of the two isotopes; 49x + 51y = 50.97 and 49x + 51x = 50.97 were common. Some students did not add the abundances of their ions to give 100 (or 1).
Text version
This question is about vanadium and some of its compounds.
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AQA 7405 · June 2025 · Paper 1 · Q8 · 17 marks
17 marks
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Most students gained two marks in part 1; a few students did not give their answer to 2 d.p. or doubled or halved the concentration of nitric acid to get their [H+]. In part 2 most students could calculate the [H+] from the pH. Students who could write the weak acid approximation generally went on to calculate the [CH3CH2COOH] correctly. Answers to parts 3 and 4 were generally good. Many students gave confused answers in part 5; those who wrote an equilibrium equation and then used that to explain the changes were more successful. Many students referred to an equilibrium but did not identify the equation, so the answer was unclear. Students who reacted their added hydroxide with the weak acid were often unsure how to proceed. Very few students mentioned the ratio of the ethanoic acid and ethanoate ion concentrations being roughly constant. Part 6 discriminated well; nearly one third of © 2025 AQA students gained all the marks. Most students calculated the moles of HA, A–, and hydrochloric acid correctly. A few students went on to correctly calculate the moles of HA and A–after the addition of the hydrochloric acid; some students added the moles of acid to both. Many students used their answers to calculate a value for the [H+] after addition and a pH of the final buffer solution. Some students lost the final mark by not giving their answer to 2 decimal places.
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This question is about acids, bases, titration curves and buffer solutions.
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AQA 7405 · June 2025 · Paper 2 · Q3 · 20 marks
20 marks
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[3.6] Students were given data about the mass of plasticiser absorbed by foods with different fat and water contents. Many could see the link between the amount of fat and the amount of plasticiser but far fewer were able identify that both fats and the plasiciser are non-polar and so form van der Waals’ forces between the molecules. The most common error was to focus on the ester links and state that the plasticiser was polar, or to say that hydrogen bonding between fat and plasiciser was the intermolecular force responsible for the trend shown.
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This question is about polymers.
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AQA 7405 · June 2025 · Paper 2 · Q5 · 11 marks
11 marks
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[5.1] Students were quite good at showing the formula of TNT having been given its IUPAC name but far fewer could balance the equation with 3HNO3 on the reactants side and 3H2O on the products side.
Text version
This question is about making 2-methyl-1,3,5-trinitrobenzene (TNT). TNT is made by reacting methylbenzene with concentrated nitric acid in the presence of concentrated sulfuric acid.
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AQA 7405 · June 2025 · Paper 2 · Q8 · 13 marks
13 marks
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[8.3] This question was well answered and students were often able to give prevention of loss of volatile liquid as a the reason a cap on the hypodermic syringe will improve the experiment.
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This question is about gas volumes. To determine Mr of volatile liquid Y, a student records the initial air volume in a gas syringe, weighs a hypodermic syringe containing Y, injects a small amount through a rubber cap into the gas syringe in an oven, reweighs the hypodermic syringe, and records final gas volume, oven temperature and atmospheric pressure. Results: initial air volume 5 cm^3; mass syringe + Y before injection 3.873 g; mass after injection 3.471 g; final gas volume 110 cm^3; temperature 155 degC; pressure 101 kPa.
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AQA 7405 · June 2025 · Paper 2 · Q9 · 11 marks
11 marks
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[9.3] This question was well answered with students being able to show they could manipulate the appropriate temperature data given to calculate 1 𝑇𝑇 in K-1 Those who got this wrong had often rounded incorrectly.
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This question is about rates of reaction. To investigate bromoalkane hydrolysis, a cross is drawn on a boiling tube. Aqueous silver nitrate is added to ethanolic RBr in the tube in a warm water bath, and the time for the cross to become invisible is recorded. The method is repeated at different temperatures.
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AQA 7405 · June 2025 · Paper 3 · Q3 · 11 marks
11 marks
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[3.2] Most students made the correct choice here.
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A student tries to measure the standard electrode potential of an Fe^3+/Fe^2+ electrode at 298 K. The attempted cell is as follows. Left half-cell: H2(g) at 100 kPa is bubbled over a Pt electrode in 1.00 mol dm^-3 H2SO4(aq). Right half-cell: an Fe electrode is placed in a solution containing 1.00 mol dm^-3 Fe^3+(aq) and 1.00 mol dm^-3 Fe^2+(aq). The two solutions are connected by filter paper soaked in NaOH(aq), and the electrodes are connected to a voltmeter.
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AQA 7405 · June 2025 · Paper 3 · Q4 · 9 marks
9 marks
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[4.1] Nearly 90% of students were able to give the correct expression for Kc with the commonest mistakes being the use of ‘+’ symbols and missing subscripts or superscripts on symbols.
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At 40 deg C, 50.0 cm^3 of 0.015 mol dm^-3 Fe2(SO4)3(aq) are mixed with 50.0 cm^3 of 0.015 mol dm^-3 KI(aq). The mixture is left for several hours until equilibrium is reached: 2 Fe^3+(aq) + 2 I^-(aq) <=> 2 Fe^2+(aq) + I2(aq). A sample is titrated to determine the amount of I^- in the equilibrium mixture.
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AQA 7405 · June 2024 · Paper 1 · Q2 · 10 marks
10 marks
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Students found parts 1, 2 and 3 challenging; fewer than 40% were successful on each of these parts. In part 1 many students suggested that the strontium hydroxide had fully dissolved or was in excess, not realising that a saturated solution was needed. Common insufficient answers in part 2 included removing the undissolved strontium hydroxide so it didn’t affect the titre, but students did not state that the titre would be larger. In part 3, very few answers referred to the solution reacting with carbon dioxide in the air; common incorrect answers stated that the solution would react with oxygen/air. Evaporation of the strontium hydroxide (solution) was accepted in the mark scheme and seen quite regularly as an answer. Answers to part 4 were very good. 33% of students gained all the marks in part 5: the question discriminated extremely well. Most students calculated the average titre: some used 3 or 4 values rather than the two concordant values. Other common errors included multiplying by 2, using an incorrect Mr and failing to multiply by 4.
Text version
This question is about an experiment to determine the solubility of strontium hydroxide in water at 20 degrees C. Solid strontium hydroxide is added to approximately 1 dm3 of distilled water in a stoppered flask kept at 20 degrees C. The mixture is checked daily and more solid is added whenever none remains. Once no more solid is needed, the mixture is filtered into another stoppered flask. A 25.0 cm3 sample of filtrate is pipetted into a conical flask, indicator is added, and the sample is titrated with 0.100 mol dm^-3 hydrochloric acid. The titration is repeated with further samples.
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AQA 7405 · June 2024 · Paper 1 · Q4 · 9 marks
9 marks
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Part 1 was answered well. 52% of students gained the mark in part 2: incorrect answers included the same number of reactants and products rather than referring to the amount, in moles, of reactants and products. ‘The units cancel’ was a common response but was insufficient for the mark. Part 3 was answered well. The calculation in part 4 was well done: errors included omitting the conversion from mole fraction into partial pressures or by giving incomplete units (kPa). Some students failed to gain a mark for the expression by omitting a symbol for partial pressure, or by using square brackets. In part 5, 73% of students gained the mark.
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This question is about some gas mixtures at equilibrium.
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AQA 7405 · June 2024 · Paper 1 · Q5 · 10 marks
10 marks
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67% of students gave a correct equation in part 1. The equation in part 2 proved more difficult: errors included HCl or HOCl as the product and a few students who had all the species correct failed to balance the equation. In part 3 most students gave the first equation. Errors in the second equation included not balancing the chlorine atoms, putting H+ on the wrong side of the equation and omitting the electrons. In the third equation 5Cl2 or 7Cl2 were common errors. A few students missed the charge on the chlorate(V) ion. In part 4, 39% of students scored both the marks: errors in the identification of the role of the chloride ion included acid, oxidising agent, reducing agent and catalyst. Students found part 5 challenging: errors included shapes with 0, 1 or 2 lone pairs or four chlorine atoms. In part 6, 24% of students gained both marks. Many students who gave the correct bond angle did not give a correct explanation: many responses referred to lone pairs repelling more than bond pairs.
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This question is about chlorine.
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AQA 7405 · June 2024 · Paper 1 · Q6 · 10 marks
10 marks
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In part 1, 15% of students scored both marks. Very few students answered in terms of the EꝊ of Zn2+. Many students referred to the EꝊ of Zn and could not gain any marks. Students who wrote about EꝊ of Zn2+ compared it to the EꝊ of VO2+ and not to the EꝊ of V3+. There was a lack of understanding of the concept that while Zn is the reacting species, the electrode potential refers to the reduction of Zn2+. Part 2 was well answered. Most students scored the mark for the cell EMF in part 3. In the cell representation, the order of VO2+ and V3+ were often the wrong way round or the Pt electrode was missing. The half- equation was often the wrong way round. The calculation in part 4 proved challenging but 34% of students managed to score all the marks. Many students used the reacting ratio correctly but then went on to use a second reacting ratio to calculate the amount, in moles, of vanadate(V) and lost the second mark. Some students used an incorrect Mr in the calculation.
Text version
This question is about vanadium ions. Use these standard electrode potentials: O2(g) + 4H+(aq) + 4e- -> 2H2O(l), E = +1.23 V; VO2^+(aq) + 2H+(aq) + e- -> VO^2+(aq) + H2O(l), E = +1.00 V; VO^2+(aq) + 2H+(aq) + e- -> V3+(aq) + H2O(l), E = +0.34 V; V3+(aq) + e- -> V2+(aq), E = -0.26 V; Fe2+(aq) + 2e- -> Fe(s), E = -0.44 V; Zn2+(aq) + 2e- -> Zn(s), E = -0.76 V; V2+(aq) + 2e- -> V(s), E = -1.20 V; Mg2+(aq) + 2e- -> Mg(s), E = -2.38 V. Here VO2^+ denotes one V atom, two O atoms and an overall + charge, whereas VO^2+ denotes one V atom, one O atom and an overall 2+ charge.
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AQA 7405 · June 2024 · Paper 1 · Q8 · 14 marks
14 marks
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Answers to part 1 were generally good: errors included confusion between ions, atoms, and molecules. 49% of students gave both correct equations in part 2: errors included missing state symbols, missing mole ratios, and missing charges. Another common error was O–(g). Many students did not give 0.5 mol of O2(g) in the equation at the start of the cycle. The calculation in part 3 was challenging: common errors were only including 1 mol of Na in enthalpy of atomisation (1 x 109), only including 1 mol of Na in first ionisation energy (1 x 494) and halving the enthalpy of atomisation of oxygen (confusing this value with bond dissociation enthalpy). Students found part 4 challenging: only 31% of students gave a correct answer. Many students identified that an electron was added to an O– ion but did not state that there is repulsion between them. There was a common misconception that electrons were being removed and the repulsion made it easier to remove the electron. In part 5 many students confused the electrostatic attraction in ionic compounds with covalent bonds and intermolecular forces. Other errors included reference to the charge density of atoms or molecules. 59% of students answered part 6 correctly: common incorrect answers included +1541 and –1541. In part 7 very few students knew that sodium oxide reacts with water: common incorrect answers included sodium oxide being insoluble in water or the reaction was too difficult to measure. The calculation in part 8 was well done by most students: common errors included using the wrong units for entropy change and not subtracting 273 to convert Kelvin into Celsius.
Text version
This question is about enthalpy changes.
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AQA 7405 · June 2024 · Paper 1 · Q9 · 17 marks
17 marks
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Errors in answers to part 1 included more shielding or more orbitals: these are correct statements but insufficient for the mark as they do not explain the increase in atomic size. The equation in part 2 was generally good: errors included missing state symbols and MgO(aq) or MgO(g) as a product. Some students gave magnesium hydroxide as a product. In part 3 most students knew that electrons were easier to lose from barium and/or that barium sulfate is insoluble. Very few students stated that a precipitate would form a layer on the barium and stop the reaction. 38% of students scored all the marks in the calculation in part 4 and most students gained a few marks. Errors included incorrect rearrangement of the equation and not using the correct mole ratio. An answer of 59 was common using a 1:1 ratio but this meant that 124 could not be subtracted and the metal could not be identified. The equation in part 5 was generally correct: errors included using H instead of H2. Very few students realised that there was ionic bonding in the compound and described metallic bonding or intermolecular forces. The correct equation in part 6 was given by 47% of students: common errors included using one mole of NaOH or not balancing the equation. 19% of students gave the correct half-equation in part 7. Li+ + e– → Li and Li+ + CoO2 → LiCoO2 were common incorrect answers. Many students identified that the reaction is reversible in part 8: some students confused the cell with a fuel cell and stated that reactants could be continuously supplied.
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This question is about metals and their compounds.
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AQA 7405 · June 2024 · Paper 2 · Q1 · 11 marks
11 marks
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[1.3] This unfamiliar mechanism question was well answered and discriminated well. The best students were able to deduce the correct curly arrows from the information given.
Text version
Propanone reacts with bromine in alkaline conditions: CH3COCH3 + Br2 + OH^- -> CH3COCH2Br + Br^- + H2O. The rate equation is rate = k[CH3COCH3][OH^-].
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AQA 7405 · June 2024 · Paper 2 · Q3 · 10 marks
10 marks
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[3.3] This was well known and over 70% scored the mark for alkenes.
Text version
This question is about hydrocarbons.
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AQA 7405 · June 2024 · Paper 2 · Q7 · 4 marks
4 marks
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7 Despite being unfamiliar, this calculation was reasonably well answered with nearly 40% gaining all four marks. A variety of methods could be used to get to the final formula and any valid working could gain full credit. Those who didn’t score the marks often worked out the mass of water and carbon dioxide formed. This could have gained credit if they went on to relate this to the mass of carbon and hydrogen in L, but students who went down this route didn’t often make this link. The best students used the mole ratio to work out how many C and H atoms there were in L. Going down this route usually led to the correct final answer although there were marks awarded for those who only got part way through. Queston 8 Synthesis and mechanism
Text version
Compound L (Mr = 88.0) contains carbon, hydrogen and oxygen only. A 6.56 x 10^-4 mol sample burns completely to form 2.62 x 10^-3 mol of H2O and 2.62 x 10^-3 mol of CO2.
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AQA 7405 · June 2024 · Paper 2 · Q11 · 9 marks
9 marks
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[11.2] An extended response question with around 40% scoring at least 3 out of 5 marks. The comparison between standard enthalpy of combustion and a value derived from calorimetry was well done. Many also appreciated that mean bond enthalpies are derived from a range of compounds, but very few recognised that a calculation based on mean bond enthalpies does not account for the enthalpy changes in the transition from a liquid to a gaseous state and vice versa.
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This question is about enthalpy of combustion.
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AQA 7405 · June 2024 · Paper 3 · Q2 · 11 marks
11 marks
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[02.4] 40% of students earned full marks for this question but some of the chosen scales made it tricky for students to plot their points correctly. Students should not be concerned about filling the whole grid as the requirement for a scale to be considered appropriate is for the plotted points to occupy more than 50% of the space available along each side of the grid. It is best to stick to values such as 2, 5, 10 units for each large square where possible. It is also not always necessary to include 0,0 on a graph scale but, in this case, many students recognised that it was a valid point as the rate would be zero if the acid concentration is zero. In 02.5, most students recognised that the line being straight was relevant to the answer, but many failed to mention that it passes through the origin. In 02.6 a majority of students were able to suggest one suitable variable but only 16% scored both marks. In many cases unsuitable suggestions such as a disappearing cross method or a colour change were suggested rather than variables relevant to this specific context.
Text version
The reaction between calcium carbonate and hydrochloric acid is monitored continuously. About 20 g of large marble chips are placed in a conical flask on a balance, 50 cm^3 of 0.4 mol dm^-3 HCl is added, a loose cotton-wool plug is placed in the neck, the balance is zeroed, and mass loss m_t is recorded every 30 s for 240 s. After completion the total mass loss m_total is recorded. A graph of (m_total - m_t) against time falls smoothly from about 0.39 g at 0 s through approximately 0.32, 0.26, 0.21, 0.17, 0.14, 0.115 and 0.093 g at 30, 60, 90, 120, 150, 180 and 210 s, to about 0.078 g at 240 s.
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AQA 7405 · June 2024 · Paper 3 · Q3 · 10 marks
10 marks
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Nearly 90% of students gained the mark for 03.1. 03.2 was another example of a slightly unusual context for this question and students needed to recognise that the units of k (s–1) were the key to identifying that the reaction is first order. 03.3 was another graph question; the scales being provided made it more accessible though there was still some misreading of the scales. In 03.4 students needed to recognise that the Arrhenius equation given in the question is of the form y = mx + c, so a plot of ln k vs 1/T will give a straight line of gradient -Ea/R. Calculating the gradient therefore leads to a value for Ea. Some students tried to substitute values into the whole equation but failed to realise that the y-axis intercept was not at 0 on the x-axis so the value of lnk at that intercept would not be equal to ln A. 03.5 tested the ability to apply information from the start of the question where the equation for the thermal decomposition of but-3-en-1-ol was given and to apply it to a different compound. Many students failed to respond to the need for a carbonyl as one of the products and suggested alcohols or acids instead.
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But-3-en-1-ol decomposes thermally by CH2=CHCH2CH2OH -> CH2=CHCH3 + HCHO. Rate constants are measured at different temperatures. The table columns are T / K, 1/T / K^-1, k / s^-1 and ln k. Rows are: 553, 1.81 x 10^-3, 4.6 x 10^-4, -7.68; 563, 1.78 x 10^-3, 8.4 x 10^-4, -7.08; 573, two missing entries, 15.6 x 10^-4; 583, 1.72 x 10^-3, 28.0 x 10^-4, -5.88; 593, 1.69 x 10^-3, 49.9 x 10^-4, -5.30.
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AQA 7405 · June 2024 · Paper 3 · Q4 · 11 marks
11 marks
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[04.6] A lack of clarity in the explanations offered again hindered things in this question although a majority of students scored one or more marks. The key for methyl orange is to recognise that its pH range (the range of pH over which it changes colour) does not match the rapid pH change on the titration curve, whereas for Universal Indicator, the problem is that there are many colour changes as the pH changes.
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At 298 K, 0.100 mol dm^-3 NaOH is added to 25.0 cm^3 of 0.0800 mol dm^-3 propanoic acid. The pH curve starts at about 2.8, rises to about 4.0 at 5 cm^3 and about 4.6 at 10 cm^3, then rises gradually to about 5.2 at 17 cm^3. It rises steeply from about pH 6 to 11 around the 20 cm^3 equivalence volume and levels near pH 12.2 by 30 cm^3.
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AQA 7405 · June 2023 · Paper 1 · Q1 · 10 marks
10 marks
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Although many students gave the correct definition in 01.1, several answers did not refer to an atom or ion and many answers gave the definition of a transition metal instead of a transition metal complex. In 01.2, the name of the shape was often not known even if the diagram was correct; common errors included diagrams with no lone pairs. Only the most able students could give the correct explanation in 01.3; many students referred to the oxidation state of Cr(PF3)6 or the PF3 molecule. In 01.4, the oxidation state was given correctly by 49% of students; the most common incorrect answer was +2. Many students gave the correct answer in 01.5; common errors were hydrogen bonds and dative covalent bonds. Many students gained partial marks in 01.6. There were several errors seen in students’ answers, eg Cl2 as a ligand, omitting the charge on the ion, drawing two cis- or two trans-isomers, and attempts at drawing optical isomers. Students found 01.7 challenging; the correct equation was given by only 14% of students.
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This question is about complexes of the transition metal chromium.
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AQA 7405 · June 2023 · Paper 1 · Q2 · 5 marks
5 marks
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The majority of students could state the purpose of the salt bridge in 02.1 but the identity of the ionic compound was not answered quite as well; several students thought that electrons flowed through the salt bridge and many students did not realise that the ionic compound should be soluble and not react with the acid or magnesium ions or chloride ions. There were many correct answers in 02.2 although a few had confused this with rates of reaction. Few students gave the correct answer in 02.3. Question 02.4 proved challenging; the equation given by most students was for the reverse reaction.
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A standard hydrogen electrode containing hydrogen gas, a platinum electrode and 1 mol dm^-3 hydrochloric acid is connected by a salt bridge and voltmeter to a magnesium electrode in 1 mol dm^-3 magnesium chloride solution. The magnesium half-equation is Mg2+(aq) + 2e- -> Mg(s), with E = -2.38 V under standard conditions.
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AQA 7405 · June 2023 · Paper 1 · Q4 · 11 marks
11 marks
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Questions 04.1 and 04.2 were well answered. In 04.3, 47% of students gained all the marks; errors included using square brackets in the expression for Kp and not rearranging the expression correctly to calculate total pressure. Most students gained at least one of the marks in 04.4; many students did not realise that changing the pressure does not change Kp. Only a change in temperature affects the value of Kp. In 04.5, many students gave correct answers; several students gave answers referring to rates.
Text version
Nitrogen dioxide decomposes at high temperature: 2NO2(g) <=> 2NO(g) + O2(g), delta H = +113 kJ mol^-1.
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AQA 7405 · June 2023 · Paper 1 · Q5 · 16 marks
16 marks
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Many students answered 05.1 well; errors included omitting 2 × –364 and forgetting to reverse the sign of one of the values given in the table. Answers to 05.2 were generally good. Students found 05.3 challenging with only 12% gaining all the marks. Many students knew that fluoride ions are smaller than chloride ions but failed to gain the mark because of confusion between atoms and ions (eg stating that “fluoride has a smaller atomic radius than chloride”). For the second mark several students referred to the attraction of F– to Oδ- or H+ instead of Hδ+. Answers to 05.4 were generally good; some students missed electrons or state symbols or put Cl2 in the top equation rather than 2 Cl. Common errors in 05.5 included missing one or both of the factors of 2 for the atomisation and the electron affinity of chlorine. A substantial number of students had problems evaluating the combination of positive and negative values. Answers to 05.6 were often vague and did not address the greater attraction between the electron removed and the more positive, smaller ion. There were some very good answers to 05.7 and 28% of students gave level 3 answers; many students began their answer by stating that the experimental values were all higher than the theoretical values and that the calcium chloride value was the highest for both the experimental and theoretical data. They then went on to explain incorrectly that this was because of covalent character in calcium chloride and that the greater difference for silver chloride was because it had more covalent character. Students who discussed the relative values for the three chlorides often lost credit because they confused atoms and molecules (eg calcium atoms are smaller than potassium atoms or calcium chloride molecules have stronger ionic bonds).
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This question is about metal chlorides, energetics and ionic bonding.
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AQA 7405 · June 2023 · Paper 1 · Q6 · 10 marks
10 marks
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Answers to 06.1 were generally good; a common error was omitting to convert the volume from cm3 to dm3. Many students found the description in 06.2 challenging. Many students did not transfer the solution from the beaker to a volumetric flask and made the solution up to 250 cm3 in the original beaker; some transferred the solution to a conical flask. Many students did not state that the beaker and stirring rod should be washed with distilled water and the washings transferred to the flask before making the solution up to the 250 cm3 mark. Several students forgot to invert the flask to ensure thorough mixing. Answers to 06.3 were good. In 06.4, most students realised that acid could continue to drip into the burette, thus affecting the titre; some students thought the titre would increase, and some thought the stem of the funnel would alter the volume by displacing acid at the top of the burette. In 06.5, 30% of students gained all the marks; common errors included using the wrong Mr of barium hydroxide, not calculating the amount in moles of barium hydroxide in 25 cm3, not realising there was a 2:1 ratio and dividing by the wrong volume to calculate the concentration. Answers to 06.6 were generally poor; many students added together the uncertainty in the pipette and the uncertainty in the burette and then divided by the total volume of both.
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The concentration of dilute hydrochloric acid can be found by titration using a standard solution of barium hydroxide.
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AQA 7405 · June 2023 · Paper 1 · Q7 · 17 marks
17 marks
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Answers to 07.1 were good. In 07.2, the correct equation was given by 35% of students; common errors included 6 waters on the LHS of the equation and missing the 2– charge on SO42–. Students generally found the explanation in 07.3 challenging; many students discussed the 3+ charge on the complex stating that the complex was polarising, with no reference to Al3+. The second mark was not often gained. Answers to 07.4 were quite good. In 07.5, the observation was often correct but the equation was less well known. A few students gave the correct answer in 07.6; Al2(SO4)3 was a common incorrect answer. In 07.7, the nitrogen atoms were generally correctly identified; common errors included circling both O species. Question 07.8 discriminated very well. Most students could calculate the amount, in moles, of Zn2+ and EDTA4– and many then subtracted correctly to get M3; common errors in answers included not multiplying by 10, not dividing by 2 and not giving the answer as an integer. Some students incorrectly calculated the Mr of Al2(SO4)3 even though this value was given in the question.
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This question is about complexes containing the aluminium ion.
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AQA 7405 · June 2023 · Paper 1 · Q8 · 5 marks
5 marks
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The half-equation required in 08.1 was often missing the electrons. In 08.2, the electrons were also often missing or on the wrong side of the equation. Many students gained the mark in 08.3; the most common incorrect answer was 1.17 V. Students found 08.4 challenging; many students thought that the cell was reversible and so could be recharged and others thought that hydrogen could be supplied from the air. Question 08.5 proved difficult for students; many referred to the flammability of hydrogen without considering that methanol is flammable too.
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In a methanol-oxygen fuel cell, CH3OH(l) + 3/2 O2(g) -> CO2(g) + 2H2O(l), and the EMF is +1.20 V.
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AQA 7405 · June 2023 · Paper 1 · Q9 · 12 marks
12 marks
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The majority of students gave a correct equation in 09.1; common errors included missing or incorrect state symbols, eg Sr(s). In 09.2, 36% of students gained all of the marks. Common errors included rearranging the equation incorrectly, not converting cm to m, not converting kg to g, incorrect use of the Avogadro constant and not giving the mass number as an integer. Question 09.3 was not well answered. Many students stated that a current was produced but did not mention the ion gaining an electron to produce the current, and many students did not state that the current was proportional to the abundance of the ion. Answers to 09.4 were generally good; a small number of students did not use the 1:2 ratio of 86Sr to 87Sr and some did not give their answer to 1 decimal place. In 09.5, many answers were insufficient and referred to the protein being denatured.
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This question is about time of flight mass spectrometry.
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AQA 7405 · June 2023 · Paper 1 · Q10 · 13 marks
13 marks
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Bromothymol blue was the most common incorrect answer in 10.1. The expression in 10.2 was well known. Answers to 10.3 were good, with 63% of students gaining all the marks. Common errors included not taking the square root or dividing by 0.1 (in M3 of the Mark Scheme) and not giving the answer to 2 decimal places. 29% of students gained all of the marks in 10.4. Many students did not identify that the reaction mixture was a buffer solution with an excess of a weak acid. These students did not subtract the amount, in moles, of sodium hydroxide from the amount of butanoic acid to determine the excess of the weak acid. Other errors included an attempt to use the weak acid approximation, [H+] = Ka × [C3H7COOH] to calculate pH. Explanations in 10.5 were generally poor; many students did not state that this was a weak acid - weak base titration and answers rarely referred to the gradual pH change; common errors included reference to the indicator having a small pH range or a gradual colour change or the equivalence point being too short. Some students made reference to there being no steep section on the graph but with no explanation about the graph to which this statement referred.
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This question is about weak acids, buffer calculations and acid-base titrations.
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AQA 7405 · June 2023 · Paper 2 · Q1 · 7 marks
7 marks
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[01.1] This unfamiliar practical question proved difficult and relatively few students scored the mark for an appreciation that the narrow neck of a conical flask will reduce the loss of droplets of liquid in a reaction giving effervescence.
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An acid reacts with excess solid sodium hydrogencarbonate, NaHCO3, in a vessel placed on a balance. The timer starts when NaHCO3 is added, and the mass of CO2 lost is recorded. A conical flask with a narrow neck is shown, open so that gas can escape. With 25.0 cm^3 of 2.23 mol dm^-3 ethanoic acid, the graph of mass of CO2 lost against time starts at (0 min, 0 g), passes approximately through (0.5, 0.7), (1.0, 1.3), (1.5, 1.8), (2.0, 2.1), (2.5, 2.3) and reaches a plateau of about 2.4 g at 3.0 min, remaining level thereafter.
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AQA 7405 · June 2023 · Paper 2 · Q2 · 5 marks
5 marks
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[02.1] Around 67% of students scored all three marks although a large proportion did so via the less efficient method of using the data from experiment 1 to calculate a k value. Despite being straight- forward the question discriminated well.
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A(aq) + 2B(aq) -> C(aq) + D(aq) is acid-catalysed and has rate equation rate = k[B]^2[H+]. At one temperature the relative initial-rate data are: experiment 1, [A] = 0.40, [B] = 0.20, [H+] = 0.10 mol dm^-3, rate = 1.00; experiment 2, [A] = 0.50, [B] = 0.20, [H+] = 0.10, rate missing; experiment 3, [A] = 0.40, [B] missing, [H+] = 0.10, rate = 0.64; experiment 4, [A] = 0.50, [B] = 0.30, [H+] = 0.06, rate missing.
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AQA 7405 · June 2023 · Paper 2 · Q4 · 15 marks
15 marks
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[04.4] The reagent and condition mark was scored by large numbers of students but the equation proved far more difficult and only just over a quarter scored full marks here. The question had a high discrimination index and identified the best students.
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Acrylonitrile, H2C=CHCN, is converted by HBr in reaction 1 into isomer W, BrCH2CH2CN. Reaction 2 converts W into NCCH2CH2CN, which reaction 3 converts into H2N(CH2)4NH2. Butane-1,4-diamine can form nylon 4,6 with hexanedioic acid.
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AQA 7405 · June 2023 · Paper 2 · Q7 · 10 marks
10 marks
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[07.3] This question proved to be more demanding than similar questions in the past because students were required to work out not only the percentage uncertainty in the mass but then to apply this to find the resulting uncertainty in the volume calculated.
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An ungraduated sealed gas syringe contains 0.146 g of propanone, Mr = 58.0, at 95 degrees C and 103 kPa. Propanone boils at 56.2 degrees C. Use R = 8.31 J K^-1 mol^-1.
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AQA 7405 · June 2023 · Paper 2 · Q8 · 19 marks
19 marks
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[08.6] The most common issue with the answers to this question was the failure to show sufficient workings. Better students showed values for the sums of the bond enthalpies for bonds broken and bonds formed. Even if a mistake was made in these values the final mark could be scored consequentially for their correct use in calculating the approximate value for the enthalpy change. Over 70% were able to score at least one of the three marks available.
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This question concerns biofuels. Palmitic acid is CH3(CH2)14COOH. Palm oil contains the triester formed when all three OH groups of glycerol react with palmitic acid. Ethanol can be made by fermentation: C6H12O6 -> 2C2H5OH + 2CO2.
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AQA 7405 · June 2023 · Paper 2 · Q9 · 12 marks
12 marks
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[09.3] This question required students to demonstrate their understanding that the Arrhenius equation could be rearranged to find the temperature for this reaction. Over half were able to score at least two of the three marks. The most common mistake was a failure to convert the activation energy given into a value in J mol–1.
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In the gas phase, ethanoic anhydride decomposes: (CH3CO)2O -> H2C=C=O + CH3COOH. Ethenone is the simplest ketene; ketenes contain one C=C and one C=O bond.
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AQA 7405 · June 2023 · Paper 3 · Q6 · 7 marks
7 marks
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In 06.1, the most common reason for a lost mark was a lack of clarity in explaining that 0.005 mol was the required amount of Ca(OH)2 needed to react with the 0.01 mol of HCl. M2 was not awarded just for seeing 0.01/2 unless it was clear why this was done. The application of a generous mark scheme in 06.2 meant that many students were able to access some marks despite quite significant misunderstanding as to what was required. Many failed to realise that the concentration of Ca(OH)2 in the saturated solution could be found directly from the solubility data given. Section B – Multiple Choice Questions Some students need to pay more careful attention to the instructions given at the start of Section B about how to complete the answers by shading in the lozenge, crossing out an incorrect answer and then circling a crossed out answer if it is then decided to be correct. There were again quite a few instances of crossed out and circled answers alongside shaded lozenges – which has to be treated as two answers and so marked incorrect. Overall, Section B proved to be rather accessible, with a mean score of 19.3 out of 30. Questions that were particularly accessible, with success rates of at least 80%, were 6, 8, 11, 14, 24, 28 and 34. The trickiest questions, where 40% or fewer students gave the correct response, were 13 and 31.
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This question concerns calcium hydroxide, neutralisation and the pH of a saturated solution. Use Kw = 6.8 x 10^-15 mol^2 dm^-6 at the stated temperature where required.
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AQA 7405 · June 2022 · Paper 1 · Q1 · 12 marks
12 marks
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In 01.1, 21% of students gained both marks; common errors included stating that the concentrations are equal or that forwards and backwards reactions are equal, without reference to rate. Many students gained the mark in 01.2. Answers to 01.3 were generally good with 68% gaining all the marks. Most students gave the correct expression in 01.4; common errors included missing p (reference to partial pressure) or using square brackets. Answers to 01.5 were good. About half the students scored both marks in 01.6; most students scored the mark for units. Some students worked out a Kp value using a rearranged expression rather than just taking the inverse of the Kp from question 01.5.
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This question is about equilibria.
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AQA 7405 · June 2022 · Paper 1 · Q3 · 17 marks
17 marks
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Most students could not give a correct equation in 03.1; if they did score the equation mark they generally carried on to complete the calculation correctly. 21% of students scored all the marks in this question. A minority had an incorrect ratio in the equation that they then used correctly in the calculation, and so scored 4 marks. The most common responses used the 3:4 ratio given in the question. Converting 5% to 100% proved challenging for many so they could not score M5. The question discriminated very well. Only the most able scored the mark in 03.2; many students referred to colour changes that were the wrong way round. Very few understood the concept of self-indicating in the titration. Most students gave the correct answer in 03.3; the most common incorrect answers were +1 and –2. In 03.4, 41% of students gave a correct equation and then carried on to score all the marks. Many students did not score the final mark as they did not use the factor of 2. Some students did not convert the volume correctly and some rearranged the equation incorrectly. In 03.5, only 5% of students gained all the marks. Most students did not give a correct definition; many referred to energy rather than enthalpy, many did not refer to 1 mol and many omitted stating that the value was averaged over many compounds. Many found processing the bond breaking/bond forming data difficult but were able to access M5.
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This question is about hydrogen peroxide, H2O2. Its oxidation half-equation is H2O2 -> O2 + 2H+ + 2e-.
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AQA 7405 · June 2022 · Paper 1 · Q6 · 15 marks
15 marks
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Most students knew the answer to 06.1. In 06.2, most students knew the equation but did not mention electrons in their explanation; many referred to oxidation numbers. Of those who mentioned electrons in the explanation, some stated that chlorine gained electrons but then thought oxygen or hydrogen lost electrons. Many students stated that a brown or purple gas was given off in 06.3 and many students did not give an ionic equation; 33% of students scored both marks. In 06.4, most students knew the role of sulfuric acid. The equations were not well known, however, and some students gave half-equations. Several students gave a correct equation for sulfur rather than a gas containing sulfur. Students found 06.5 challenging; 10% scored all the marks in the question. Carbon dioxide was scored more often than the other marks. Many students could not give the equation and many thought the sodium halide was NaCl. 36% of students gained all three marks in 06.6. Many students gave structures with only one lone pair and explanations often stated that the lone pairs and bond pairs repelled each other without stating that the lone pair-lone pair repulsion was greater then the bond pair-bond pair repulsion. Common incorrect bond angles were 120o and 180o. About half the students gave a correct equation in question 06.7; common errors included the wrong formulas for titanium chloride and magnesium chloride and using Mg2 in the equation.
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This question is about Group 7 elements and their compounds.
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AQA 7405 · June 2022 · Paper 1 · Q8 · 6 marks
6 marks
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Less than half the students gave a correct answer in 08.1; Zn was a common incorrect response. In 08.2, few students realised that the porous separator was acting as a salt bridge; a common misconception was that it was ‘separating reactions’ or ‘stopping electrolyte & paste mixing’. The equation in 08.3 was not answered well; 29% of students gained this mark. Many students gave the reverse equation or gave a correct one but did not cancel the water and hydroxide ions. Question 08.4 was very challenging; only 7% scored both marks. Many students calculated the standard electrode potential correctly although common errors were – 0.4 V and 2.06 V. In 08.5, most students did not realise that the overall equation for the cell reaction is the same in each cell.
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This question is about non-rechargeable cells, rechargeable silver-zinc cells and hydrogen-oxygen fuel cells.
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AQA 7405 · June 2022 · Paper 2 · Q1 · 21 marks
21 marks
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[01.8] This question had a very high discrimination index and the best students were able to score full marks. Common errors included poor drawing of curly arrows and mistakes in the structure of the intermediate.
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Acidified butanone reacts with iodine: CH3CH2COCH3 + I2 -> CH3CH2COCH2I + HI.
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AQA 7405 · June 2022 · Paper 2 · Q2 · 11 marks
11 marks
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[02.2] This was a very straightforward equilibrium constant expression that the vast majority of students were able to answer correctly.
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Tetrafluoroethene is made by 2CHClF2(g) <=> C2F4(g) + 2HCl(g), delta H = +128 kJ mol^-1. Initially 2.00 mol CHClF2 is placed in 23.2 dm3; at equilibrium 0.270 mol remains.
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AQA 7405 · June 2022 · Paper 2 · Q5 · 12 marks
12 marks
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[05.2] Removal of water-soluble impurities as the correct reason for adding distilled water was less well known.
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Hexan-2-ol is immiscible with water and boils at 140 degrees C. It is prepared by adding concentrated phosphoric acid to 11.0 cm3 hex-1-ene in an ice bath, adding water, separating and washing the organic layer with water, drying with anhydrous MgSO4, filtering under reduced pressure, then distilling and collecting 130-160 degrees C.
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AQA 7405 · June 2022 · Paper 2 · Q9 · 12 marks
12 marks
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[09.5] The question demanded that students show their working. Whilst it was well answered overall, many failed to score both marks. The first mark required students to show that the Mr was one less than 345, but this was often omitted despite the question stating that each molecule gains a hydrogen ion (H+) during electrospray ionisation.
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Olive oil is 85% by mass of unsaturated triester Y, C57H100O6, Mr 880, plus inert impurity. Each Y molecule contains five C=C bonds. A weighed oil sample is made to 250 cm3 with inert solvent, and 25.0 cm3 portions are titrated with 0.025 mol dm^-3 Br2(aq).
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AQA 7405 · June 2022 · Paper 3 · Q2 · 6 marks
6 marks
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This levels of response question was expected to be more accessible than some in the past but a lack of accuracy in describing the tests for the anions meant that Level 3 was rarely attained. The need to warm after adding NaOH when testing for NH4+ was often missing as was the need to acidify the BaCl2 when testing for sulfate. Many students also stopped their description of the test for Al3+ at the stage of forming a white precipitate and failed to mention that it redissolves in excess NaOH. The equations for the test for Al3+ should preferably have been those with the hydrated ion but the simpler versions were allowed from the point of view of indicative content. The equation for the redissolving of the solid was often shown as Al(H2O)3(OH)3 + OH– → Al(OH)4– + 3 H2O which implies a combination of ligand replacement and acid-base behaviour, but the product anion should be shown with two water ligands still present in this case. In stage 1 the empirical formula of NH28AlS2O20 was sometimes not actually shown even though the calculation was done. Some students seemed confused that, in this case, the empirical formula mass is equal to the relative formula mass and they thought that meant that x = 0. It was hoped that students would recognise that 1 × N meant one NH4+ and 2 × S meant two SO42– ions – from which the number of waters could be found.
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Tschermigite is a hydrated, water-soluble mineral of relative formula mass 453.2, represented by M.xH2O where M contains all ions. Table 4 gives percentage composition by mass: N 3.09%, H 6.18%, Al 5.96%, S 14.16%, O 70.61%. Analysis indicates NH4+, Al3+ and SO4^2- ions.
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AQA 7405 · June 2022 · Paper 3 · Q4 · 10 marks
10 marks
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Most students accessed M1 in 04.1 but M2 was often not awarded due to the absence of ‘frequency’ or of ‘successful’. Just referring to ‘more collisions’ is not enough. Drawing tangents by eye is not an exact science so a reasonable range of answers was accepted here with the key factors being that the tangent needed to touch the curve at 0.05 and not cross the curve at any point. Students are encouraged to choose a reasonable range for the ẟx and ẟy used in the calculation of gradient and to read the scales carefully. Most students were able to select the appropriate values for the calculation in 04.3 although reading the scale was a pitfall for some, with 0.83 often seen as the initial concentration. In 04.4, apart from some continued issues with reading of the scales, the plots were mostly accurate. In 04.5, the plots in 04.4 should have led to the statement that the reaction is first order – and this was seen in most answers, but M2 was less often awarded. To fully justify first order, the line needs to be referred to as ‘straight’ and ‘through the origin’. If, instead, students choose to refer to ‘doubling the concentration causing a doubling in rate’ they need to select and quote data from the graph to support this.
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Hydrogen peroxide decomposes as 2H2O2(aq) -> 2H2O(l) + O2(g), catalysed by MnO2. Oxygen is collected every 10 s for 100 s. Figure 1 plots [H2O2] against time: approximate points are (0,0.083), (10,0.061), (20,0.0465), (30,0.0345), (40,0.026), (50,0.0195), (60,0.0145), (70,0.0105), (80,0.0075), (90,0.0048), (100,0.0032), with a smooth decreasing curve. The axes span 0-100 s and 0.00-0.09 mol dm^-3.
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AQA 7405 · June 2022 · Paper 3 · Q5 · 11 marks
11 marks
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05.1 was well answered by most students. In 05.2 many students either did not notice that there were six marks available or were not able to work out how to access them as many answers were very brief and generic. The question specifically asked for suitable equations to be included but these were often left out of answers. 05.3 saw the greatest evidence of confusion in the use of correct terminology. One of the key aspects of the topic on electrochemistry and electrode potentials is its reliance on conventional terms of reference. When referring to an electrode potential it is advised that students stick to the conventional form. e.g. Eo S2O82–/SO42– is greater than Eo Co3+/Co2+ Therefore any references to electrode potentials and half-cell equations should follow the convention of showing (or implying) a reduction in the forward direction. A commonly seen example of a lack of clarity was “The electrode potential for Co2+ is less than that for S2O82– but more than for iodide so it can oxidise one and reduce the other.” Apart from the reference to “The electrode potential for Co2+” being incorrect it is not clear from this what is oxidising or reducing what. This is a particular example of a situation where references to ‘it’ are likely to be ambiguous. Many answers were also difficult to mark because of carelessness with CO instead of Co and confusion between subscripts and superscripts e.g. CO3+ Section B – Multiple Choice Some students need to pay more careful attention to the instructions given at the start of Section B about how to complete the answers by shading in the lozenge, crossing out an incorrect answer and then circling a crossed-out answer if it is then decided to be correct. There were quite a few instances of crossed-out and circled answers alongside shaded lozenges – which has to be treated as two answers and so marked incorrect. Questions students found particularly straightforward, with correct answers from at least 80% of the cohort, were B32, B34, B18, B25, B23. Questions that proved to be particularly challenging were B10, B33, B28, B7.
Text version
This question concerns heterogeneous, auto- and homogeneous catalysis. Table 6 gives standard reduction potentials: S2O8^2- + 2e- -> 2SO4^2-, +2.01 V; Co3+ + e- -> Co2+, +1.82 V; I2 + 2e- -> 2I-, +0.54 V.
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AQA 7405 · November 2021 · Paper 1 · Q1 · 11 marks
11 marks
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Most students could not recall the definition in question 01.1; students rarely referred to constant pressure and many referenced energy but not heat. Question 01.2 was generally well answered; common errors involved lack of balancing charges and omission of state symbols. In question 01.3 many students missed one or both factors of 2. Students found question 01.4 challenging; errors included lack of state symbols, equations written the wrong way around, enthalpy of lattice dissociation or formation equations, and equations with water not cancelled out. Many students answered question 01.5 well. Common errors in answers, however, included the wrong sign for the enthalpy change and omitting the factor of 2. Few students scored both marks for question 01.6; common errors included discussing the atomic radii of the ions, shielding and the distance of outer electrons to the nucleus. Very few students discussed the attraction of the ion to water.
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This question is about enthalpy changes for calcium chloride and magnesium chloride.
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AQA 7405 · November 2021 · Paper 1 · Q2 · 6 marks
6 marks
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Many students answered question 02.1 well; a few students discussed the mass instead of the mass number, and some gave a definition of relative atomic mass. In question 02.2, the most frequent error was the number of electrons in the ion. A significant number of students were unable to produce an appropriate algebraic expression in question 02.3 and many did not include a term for the 48Ti isotope. Those who could write a correct expression went on to give the percentage of the 48Ti isotope and didn’t give the percentage of the 46Ti isotope. Only the most able scored all the marks in this question.
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This question is about isotopes of titanium.
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AQA 7405 · November 2021 · Paper 1 · Q3 · 12 marks
12 marks
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Some students omitted the state symbols from the equation or missed out one of the state symbols in an otherwise correct equation in question 03.1; some students incorrectly gave oxygen or sodium oxide as a product. Most students appreciated that the reaction would be more violent and that the glass might shatter. In question 03.2 some students started from P2O5 and some gave H3PO3 as a product. Many gave the pH to be 2 which wasn’t low enough to be given a mark. Answers to question 03.3 were generally quite good. The structure and bonding in silicon dioxide was generally well done but some students discussed forces between silicon dioxide molecules. The structure for phosphorus(V) oxide was less well known; the term molecular was given only in the best answers. Some students did not state that van der Waals’ forces were between molecules. Students found question 03.4 challenging. A range of answers was seen for the oxide; students who gave the correct formula of aluminium oxide often failed to give a correct balanced equation. Question 03.5 was answered well, though common errors included calcium hydroxide or an incorrect formula for magnesium hydroxide. Although many students gave the correct answer in question 03.6, chlorine and argon were common incorrect answers.
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This question is about Period 3 elements and their compounds.
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AQA 7405 · November 2021 · Paper 1 · Q4 · 25 marks
25 marks
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In question 04.1 most students stated that a heterogeneous catalyst is in a different phase to the reactants or described what a catalyst is or how it works. Students gave better answers for stage 2 than for stage 3; in stage 3 many students knew that active sites were blocked but did not state that this was poisoning and didn’t explain how the efficiency of the catalyst could be improved. Several students confused the efficiency of the catalyst with conditions needed to maximise the yield or to speed up the reaction. In question 04.2 most students stated that ions of the same charge would repel, but fewer stated that the activation energy would be high. The equations were not well known. In question 04.3 many students stated that zinc had a full d sub-shell or had 3d10 configuration but did not explain how that related to the oxidation states of zinc. Some students completed the calculation well in question 04.4; common errors included identifying the limiting reagent as iron and then using the amount of iron (in moles) in the calculation, or stating that hydrochloric acid was the limiting reagent but not realising that this then controlled the amount of hydrogen produced. Some students converted the temperature and pressure incorrectly. In question 04.5 the colour of iron(II) carbonate was well known; however, if iron carbonate was given in words the (II) was often missing. The colour and/or formula were generally known in question 04.6 but the equation was not answered well; if the species were correct the equation was often not balanced. Students found question 04.7 very challenging; students often discussed the charge-to-size ratio of the hydrated ions rather than the iron ions themselves. Students rarely gained the second mark but a few did state that more hydrogen ions were released and so gained the third mark.
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This question is about iron, catalysis and iron ions in aqueous solution.
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AQA 7405 · November 2021 · Paper 1 · Q5 · 11 marks
11 marks
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Question 05.1 was generally well answered. Some students did not gain the first mark because they did not state a change in yield; a common error was to refer to equilibrium shift. Many students did not gain the third mark as they did not refer to the equilibrium shifting to oppose the decrease in pressure. About half of the students answered question 05.2 very well but others found the question very challenging; many students could not calculate the amount, in moles, of SO2 and O2 at equilibrium or omitted the amount of SO3 when calculating the total amount, in moles, at equilibrium. Although question 05.3 was often well answered, common errors included not giving an expression for Kp, or giving an expression for Kp that used square brackets instead of partial pressures. Many students did the calculation well but some failed to use the squared terms from their expressions; units were sometimes given as concentrations rather than in terms of kPa. Just over half the students gave the correct answer in question 05.4.
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This question is about 2SO2(g) + O2(g) <=> 2SO3(g).
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AQA 7405 · November 2021 · Paper 1 · Q6 · 16 marks
16 marks
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Students found question 06.1 challenging; many students stated that [H2O] is 1 or [H2O] has no effect. Some students appreciated that the concentration of water is included in the equilibrium constant. In question 06.2 some students realised that the reaction was endothermic but did not complete their answer with an explanation. Some students tried to explain their answer in terms of kinetics. Answers to question 06.3 were generally well done; a few students used ( ) brackets in the expression rather than [ ] brackets and a few students did not give the pH to two decimal places. Some students could not give a correct explanation. Almost all students answered question 06.4 correctly. In question 06.5 most students knew that the solution would be contaminated. Students found question 06.6 very challenging; most students said the titration would be more precise or accurate. Very few students explained clearly that a small volume of added alkali gives a large change in pH. In question 06.7 many students related the colour changes to the equivalence point or the endpoint without using the curve. Most students calculated the amount of hydrogen and hydroxide ions correctly in question 06.8; common errors, however, included not calculating the excess amount of hydroxide ions and not dividing by the volume of solution.
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This question is about water dissociation, pH measurement and acid-base titration.
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AQA 7405 · November 2021 · Paper 1 · Q7 · 9 marks
9 marks
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In question 07.1 most students explained that gases are more disordered; a few students explained the disorder in terms of the number of atoms in the molecule rather than using the physical state of the substances. Answers to question 07.2 were poor; common errors included 0 with no units, 298 K and +/-273 K. Question 07.3 discriminated well. Several students reversed the expressions for change in enthalpy and change in entropy and gained negative values; some students did not convert the change in entropy to the correct units and some tried to convert the temperature in Kelvin into degrees Celsius. Most students could give a correct expression involving ΔH, ΔS and T.
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For 2Al2O3(s) + 3C(s) -> 4Al(s) + 3CO2(g), thermodynamic data are: Delta f H in kJ mol^-1, Al2O3 -1669, Al 0, C 0, CO2 -394; S in J K^-1 mol^-1, Al2O3 51, Al 28, C 6, CO2 214.
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AQA 7405 · November 2021 · Paper 1 · Q8 · 8 marks
8 marks
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Few students gave a correct answer to question 08.1; some students explained that it was a list of electrode potentials but failed to state that these were in order and a few students used the idea of EMF or cell potentials rather than electrode potentials. Conditions in question 08.2 were well known but some students only gave one condition; 101 kPa or 1 atm were the commonest wrong answers. In question 08.3 many students gave [Co(H2O)6]3+ as the ion; Fe was also a common incorrect answer. In question 08.4 many students did not start with Fe but with [Fe(H2O)6]2+; those who started with Fe often gave Fe2+ or [Fe(H2O)6]2+ as the product. Students who gave an equation often failed to cancel out the waters on each side of the equation. Very few students gave the explanation correctly in question 08.5. Some students gave the equation correctly; a significant number, however, thought the cobalt complex was a reducing agent and gave iron as the product. In question 08.6 many students realised that the ligands were different.
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Electrode potentials in V include Fe2+/Fe -0.44, H+/H2 0.00, [Co(NH3)6]3+/2+ +0.11, Fe3+/Fe2+ +0.77, VO2+/VO^2+ +1.00 and [Co(H2O)6]3+/2+ +1.81. For vanadium, VO2+ (two O atoms, charge +1) + 2H+ + e- -> VO^2+ (one O atom, charge +2) + H2O.
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AQA 7405 · November 2021 · Paper 1 · Q9 · 7 marks
7 marks
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Students found question 09.1 very challenging. Some students stated that lithium reacts with water but only a very small number of students could give an explanation in terms of electrode potentials. Answers to question 09.2 were generally correct. In question 09.3 some students realised that the cell was operating under non-standard conditions. Many students could calculate the oxidation state in question 09.4; however common errors included –7 and +9. Very few students knew the equation in question 09.5. The equation in question 09.6 was slightly better, but many students reversed the equation and some had electrons on the wrong side of the equation.
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This question is about lithium cells. Standard electrode potentials in V are Li+/Li -3.04, 2H2O/H2,OH- -0.83 and I2/I- +0.54.
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AQA 7405 · November 2021 · Paper 2 · Q1 · 15 marks
15 marks
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All aspects of this question differentiated very well. The extended calculation in question 01.3 attracted good responses with a third of the students gaining full marks and the majority able to access at least 1 or 2 marks. A common mistake was to assume that the oil was pure triester. In question 01.4 very few students appreciated that aqueous ethanol was used as a mutual solvent for both the oil and the potassium hydroxide.
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Coconut oil contains a triester with three identical R groups. This triester reacts with potassium hydroxide.
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AQA 7405 · November 2021 · Paper 2 · Q2 · 19 marks
19 marks
$AQA 7405 · November 2021 · Paper 2 · Q2 · 19 marks — This question covers petrol fractions, cracking, infrared absorption by carbon dioxide, removal of CO2 with 2-aminoethanol and the environmental case for bioethanol.$
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In this question a surprisingly small proportion of students were able to state the meaning of the term fraction. In addition, very few were able to explain why C=O bonds in carbon dioxide absorb infrared radiation. A good range of answers was seen for the extended response question about the environmental impact of bioethanol as a fuel, but a significant number of students were unable to get started here.
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This question covers petrol fractions, cracking, infrared absorption by carbon dioxide, removal of CO2 with 2-aminoethanol and the environmental case for bioethanol.
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AQA 7405 · November 2021 · Paper 2 · Q4 · 9 marks
9 marks
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Question 04.1 gave a good range of scores and a third of students were able to score at least 2 marks. The common errors included multiplying the value of enthalpy of atomisation for hydrogen by 3 rather than 6. Question 04.3 required students to apply mechanistic ideas to structures that were provided. The vast majority of students were able to score some marks on this question and it also proved to be a very good discriminator.
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Figure 3 compares delocalised benzene(g) with hypothetical Kekule cyclohexa-1,3,5-triene(g). Benzene formation from 6C(s) + 3H2(g) has Delta H1 = +83 kJ mol^-1. Table 1: atomisation C +715, atomisation H +218, C-C +348, C=C +612, C-H +412 kJ mol^-1.
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AQA 7405 · November 2021 · Paper 2 · Q5 · 7 marks
7 marks
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The algebraic approach needed in question 05.1 proved difficult for some but around half the students were able to score full marks here. The structure of the diester in question 05.2 was very poorly answered, but the familiar Kc calculation in question 05.3 proved very accessible and around two thirds of students scored all three marks.
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Diester hydrolysis: C7H12O4 + 2H2O <=> 2CH3COOH + HO(CH2)3OH.
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AQA 7405 · November 2021 · Paper 2 · Q8 · 13 marks
13 marks
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Few students scored 3 or more marks on question 08.2. Both the reagents and equations proved very challenging, with over 50% either failing to score or not attempting this question. A very good range of marks was seen for question 08.3 and the question discriminated very well.
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Synthesis scheme: cyclohexanol -> cyclohexene -> compound G -> cyclohexane-1,2-diol -> cyclic diester with ethanedioyl dichloride.
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AQA 7405 · November 2021 · Paper 2 · Q10 · 12 marks
12 marks
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The idea of using an excess of NaHCO3 to quench the reaction was not well understood and few students scored both marks for question 10.1. Whilst some students were able to explain that the concentration of propanone was effectively constant in question 10.2, few were explicit enough about the concentration of propanone being much larger than the concentration of iodine. Question 10.3 was very straightforward and, as a result, did not differentiate well. Half the students scored at least some of the marks for the calculation in question 10.5 based on the Arrhenius equation. Concluding Remarks Overall the questions in this paper proved to be of a similar demand to those in previous series. The paper differentiated well, and students were able to complete the questions in the time available. All questions were correctly answered by a good number of students.
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Acid-catalysed iodination: CH3COCH3 + I2 -> CH3COCH2I + HI. The method uses 25 cm3 1.0 M propanone, 10 cm3 1.0 M HCl and 25 cm3 5.0 x 10^-3 M I2. One-minute samples are quenched in excess NaHCO3 then titrated with thiosulfate. Table 5 gives time/minute and thiosulfate volume/cm3: (1,41), (2,35), (3,24), (4,22), (5,16), (6,10).
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AQA 7405 · November 2021 · Paper 3 · Q5 · 5 marks
5 marks
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Most students were able to make a start on this calculation and many earned two marks for simply converting pH to [H+] and pKa to Ka even if they could not get any further. There was evidence of confusion between ‘concentration’ and ‘amount’ with a significant number of students converting the given concentration of methanoic acid into an amount and then trying to substitute that amount into the expression for Ka instead of using the given concentration.
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A buffer is made from 25.0 cm^3 of 0.100 mol dm^-3 methanoic acid and solid sodium methanoate. For methanoic acid, pKa = 3.75 at 298 K. The target pH is 4.05 and the solution volume is assumed constant.
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AQA 7405 · November 2021 · Paper 3 · Q6 · 13 marks
13 marks
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Practical weaknesses and insufficient precision in answers let many students down here. Question 06.1 specifically asked for safety concerns related to the apparatus diagram, with the hope that students would recognise that the bung should not be present (as it would mean a sealed apparatus is being heated) and that the flask is not clamped. Vague references to ‘the clamp being in the wrong place’ were not sufficient because a more specific response was needed. Many students referred to the direction of the water flow being wrong because it should enter at the bottom of the condenser – but this is not a safety concern so could not be credited here. However, if it was mentioned in 06.1 but not then mentioned in 06.3, credit was still allowed for 06.3. In question 06.3 many students failed to recognise that the thermometer is not needed at all and got confused with distillation by suggesting that the thermometer needed to be higher up in the apparatus. Section B The mean score on Section B was 17.7 out of 30 (59%). The five most straightforward questions (answered correctly by more than 80% of students) proved to be B7, B10, B22, B23 and B28. The five most challenging questions (answered correctly by fewer than 40% of students) were B12, B15, B25, B26 and B31. Multiple-choice items that discriminated particularly well (i.e. there was a good correlation between performance on the item and overall performance on the paper) across the range of ability of the students were B8, B21, B29, B30, B33 and B34. Multiple-choice items that did not discriminate very well at all were B12 and B15.
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A student plans to oxidise propan-1-ol to propanoic acid. Figure 4 shows a heated round-bottomed flask containing propan-1-ol, potassium dichromate(VI) and small glass beads, below a vertical condenser. Only the condenser is clamped; a bung seals its top around a thermometer extending into the flask; cooling water enters at the top and leaves at the bottom.
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AQA 7405 · November 2020 · Paper 1 · Q1 · 10 marks
10 marks
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Many students failed to gain a mark in part 01.1 by failing to divide their final answer by two. In 01.2, many different answers were seen; some students did correctly match the lattice energies to the correct substance. Most students gave the correct answer in 01.3. Question 01.4 was more challenging; many students failed to gain the first mark by referring to atoms rather than ions. Very few students explained that the attraction between the positive ion and a water molecule is due to the δ– charge on the oxygen of the water molecule or to the oxygen’s lone pair. In 01.5, many students gained all the marks but some students could not construct a correct cycle and therefore struggled.
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This question is about lattice, hydration and solution enthalpies.
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AQA 7405 · November 2020 · Paper 1 · Q2 · 15 marks
15 marks
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02.1 was not well answered; common incorrect answers often omitted reference to the average mass of an atom. In 02.2, most students deduced that the percentage of the missing isotopes added up to 13.9, but many students were unable to write an expression in terms of one unknown and could make no further progress. Most students who calculated a value of the abundance for one isotope could find the percentage of the other. Most students answered 02.3 well. In 02.4, most students stated that there had to be ions for detection but fewer talked about the need for acceleration; some students failed to gain marks through giving incorrect detail, eg acceleration by a magnetic field. Although many students scored full marks in 02.5, common errors included a failure to calculate the mass of the ion in kg or a failure to use the Avogadro number correctly. The kinetic energy was often transcribed incorrectly.
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This question is about chromium isotopes and time-of-flight mass spectrometry.
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AQA 7405 · November 2020 · Paper 1 · Q3 · 7 marks
7 marks
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Students were about equally divided over whether the second ionisation energy would be higher or lower than that of aluminium in 03.1. There were many different answers in 03.2; argon, sulfur and chlorine were common wrong answers. In the equation the state symbols were often difficult to read and therefore ambiguous, so could not score the mark; sometimes the state symbols were missing. 03.3 was generally well answered. The increase in nuclear charge was well known but the similarity in shielding less so. Answers to 03.4 were well done. In 03.5, many students gave P2O5 instead of P4O10 as the product and some students did not attempt to balance the equation.
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This question is about Period 3 trends and compounds.
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AQA 7405 · November 2020 · Paper 1 · Q4 · 12 marks
12 marks
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Most students scored the mark in 04.1. Answers to 04.2 were well done but some students omitted the square brackets. Students found 04.3 more challenging. Often the concentration of the diluted acid was incorrect and some students failed to take a square root in their calculation. Most students could convert their concentration of H+ ions to a pH. Some students scored full marks in 04.4 but for many the question presented several challenges. Most students correctly calculated the concentration of H+ ions but then could not rearrange the expression to calculate the concentration of propanoate ions. Some students failed to notice that only 500 cm3 of the buffer solution was used and a few did not use the correct Mr for sodium propanoate.
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Propanoic acid, C2H5COOH, is weak; Ka = 1.35 x 10^-5 mol dm^-3 at 25 degrees C.
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AQA 7405 · November 2020 · Paper 1 · Q6 · 11 marks
11 marks
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In 06.1, students often failed to mark the cross with sufficient accuracy; many students did not put the cross on the correct axis but, instead, on the curve or on the wrong axis. Many students failed to calculate correctly the amount, in moles, of hydrogen at equilibrium in 06.2. However, most students could take their mole fraction and find the partial pressure correctly. Most students gave the expression correctly with correct units in 06.3; some students expressed the equilibrium constant in terms of concentrations rather than partial pressures with appropriate units, and failed to score any marks. In 06.4, many students who gave the correct answer that the partial pressure of methanol increased thought this was because Kp also increased. Many students knew that Kp was unchanged in 06.5 but then failed to explain the reason fully; common errors included that a catalyst increases the rate of both reactions or lowers the activation energy by providing an alternative route.
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Methanol is made by CO(g) + 2H2(g) <=> CH3OH(g), Delta H = -91 kJ mol^-1.
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AQA 7405 · November 2020 · Paper 1 · Q7 · 6 marks
6 marks
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Most students could work out the number of bonding pairs and lone pairs in the compounds; students who drew structures scored better generally than students who did not. More able students then went on to write correctly about intermolecular forces; most understood that XeF4 has stronger intermolecular forces because the molecule is bigger. Only the very best students realised that PF3 has dipole-dipole forces between molecules and these must nevertheless be weaker than the van der Waals intermolecular forces in XeF4.
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The melting point of XeF4 is higher than that of PF3.
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AQA 7405 · November 2020 · Paper 1 · Q8 · 8 marks
8 marks
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Many students scored full marks in 08.1 but for some the question proved challenging. Most students calculated the amount in moles of thiosulphate correctly and many then went on to calculate the amount in moles of iodine; some introduced incorrect ratios to determine the amount of chlorate(I). Many students assumed that the volume of the diluted solution was 250 cm3 and not 100 cm3, as stated in the question, and multiplied by the wrong factor. Some students used the Mr of ClO– rather than NaClO and some were unable to use the density to work out the mass of the original sample. Many students correctly answered 08.2.
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A bleach analysis converts ClO- to I2, then titrates I2 with thiosulfate. A 10.0 cm3 bleach sample is diluted to 100 cm3; 25.0 cm3 uses 33.50 cm3 of 0.100 mol dm^-3 S2O3^2-. Density of original bleach is 1.20 g cm^-3. Equations: ClO- + 2H+ + 2I- -> Cl- + H2O + I2; 2S2O3^2- + I2 -> 2I- + S4O6^2-.
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AQA 7405 · November 2020 · Paper 1 · Q9 · 9 marks
9 marks
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Most students knew there would be no reaction and therefore no visible observation in 09.1; the most common incorrect answer was a white precipitate. In 09.2, most students gave a correct observation and the correct equation was often seen; the role of the chloride ion was less well understood. Students found 09.3 more challenging; only a few students gave a correct equation. The explanation was not well done. Although some students gave the oxidation states correctly, they either failed to identify the oxidation or reduction processes or they gave them the wrong way round; many students thought hydrogen was the element being reduced or oxidised. In 09.4, many students incorrectly gave the colour of bromine as a brown solution and some students failed to gain marks by simply stating a colour but omitting to state that a solution formed. Many students were unable to write a correct ionic equation; some students gave an unbalanced ionic equation and some gave a full equation including sodium ions.
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This question is about reactions of sodium halides.
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AQA 7405 · November 2020 · Paper 1 · Q10 · 11 marks
11 marks
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In 10.1, many students calculated the enthalpy change incorrectly as +49 kJ mol–1. There were several different answers calculated for the entropy change and a few students omitted the conversion into kJ. Most students knew the equation for the Gibbs free energy change and were thus able to calculate a value for the Gibbs free energy change with their values. Students found 10.2 challenging. Some students realised that the y-intercept was equal to the ΔH of the reaction and knew that the gradient was –ΔS; these students read the axes carefully and calculated values for the thermodynamic quantities. A few students interchanged the values for ΔH and ΔS. Most students knew that a negative ΔG meant that a reaction would be feasible in 10.3. Students often failed to gain the mark by giving a temperature of 840 K or below or, less commonly, above 860 K.
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For CO2(g) + 3H2(g) <=> CH3OH(g) + H2O(g), Delta f H values in kJ mol^-1 are CO2 -394, H2 0, CH3OH -201, H2O -242; entropies in J K^-1 mol^-1 are 214, 131, 238 and 189 respectively.
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AQA 7405 · November 2020 · Paper 1 · Q11 · 6 marks
6 marks
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Most students found this question challenging. Most students were unable to give a correct equation in 11.1 and 11.2; some students wrote the correct substance on the correct side of the equation but then added electrons to the wrong side. In 11.3, most students gave an unbalanced equation; some students reversed the equation and gave the equation for photosynthesis and some students failed to cancel out water molecules on each side of the equation. 11.4 was the most challenging question on the paper. Very few students suggested the correct substance for the electrode and students seldom gave the reduced and oxidised species in the correct order. Some students gave a correct answer in 11.5. Incorrect answers included use of a salt bridge, use of standard conditions, replacing electrodes and adding more oxygen or water.
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In an acidic glucose-oxygen fuel cell, glucose and water form CO2 and H+ at the negative electrode; O2 and H+ form water at the positive electrode.
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AQA 7405 · November 2020 · Paper 2 · Q1 · 11 marks
11 marks
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The majority of the question was well done. Many of the students scored well on 01.1 and 01.5. Students found it hard to express the relationship between initial concentration and reaction time in 01.2 but most were able to deduce the order from the data given. Apparatus diagrams were very varied and it was clear that some students were unable to draw a cross-sectional diagram well.
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Phosphinate ions react with hydroxide: H2PO2- + OH- -> HPO3^2- + H2.
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AQA 7405 · November 2020 · Paper 2 · Q4 · 16 marks
16 marks
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This question covered the skills learned in completing required practical 10 but a surprising number of students were unable to suggest re-weighing the weighing boat as the missing step in the method for 04.1. Few students appreciated the need to state an appropriate size for the apparatus to be used to measure out the ethanoic anhydride in 04.2. The calculation in 04.5 was very well answered. Students were often able to identify that impurities lower the melting point of a sample in 04.6 but far fewer appreciated that impurities also broaden the range of temperatures over which the impure sample melts. In 04.7, many students were able to suggest keeping the mixture away from naked flames but far fewer identified that keeping the mixture below the boiling point of ethanol would also be an appropriate precaution to take. 04.8 proved difficult and only the best students explained that washing the aspirin with cold ethanol would be done to remove soluble impurities. 04.9 was well answered.
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Aspirin is prepared by reacting salicylic acid with ethanoic anhydride, using concentrated phosphoric acid, cooling, filtering and recrystallising from ethanol.
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AQA 7405 · November 2020 · Paper 2 · Q8 · 9 marks
9 marks
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Fewer than 10% of students scored 4 or 5 marks for the calculation in 08.1, but the first three marks proved much more accessible. Students were often unable to link the amount in moles of CO2 produced in combustion to the amount of carbon in the original sample. Even fewer were able to do this to determine the amount in moles of hydrogen from the amount of water produced. 08.2 proved more accessible and many students scored both marks, with a variety of methods used. 08.3 was well answered but 08.4 was only scored by around 40% of students.
Text version
Citric acid hydrate is H3Y.xH2O; anhydrous citric acid has displayed structure HOOC-CH2-C(OH)(COOH)-CH2-COOH.
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AQA 7405 · November 2020 · Paper 2 · Q9 · 18 marks
18 marks
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The first two parts of the question were very well answered and students often scored high marks. 09.3 was much less well answered, with fewer than 20% of students able to suggest that the concentration of water being effectively constant is the reason why the equilibrium expression can be written without including it. 09.4 was another calculation where many students got started but few were able to access the highest marks. Only the very best identified that an algebraic approach was needed to calculate the required equilibrium concentration. 09.5 required students to apply their understanding of standard mechanistic ideas to a novel mechanism. Most students were able to score at least some of the marks and a good number (44.3%) scored all three marks. Full marks proved far more difficult in 09.6 but students often gained some credit for recognising that the alkyl group would be electron donating. Concluding Remarks Overall the questions in this paper proved to be of a similar standard to those in previous series. The paper differentiated well, and students were able to complete the questions in the time available. All questions were correctly answered by a good number of students apart from 07.3 which was the most difficult question on the paper.
Text version
A(aq) + 2B(aq) <=> C(aq), followed by equilibria for hydration of chloroethanal.
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AQA 7405 · November 2020 · Paper 3 · Q3 · 11 marks
11 marks
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In 03.1, a majority of students were able to score 2 or more marks but many answers were rather muddled. There was often a failure to appreciate that only certain wavelengths or frequencies of light are absorbed (to excite d sub-shell electrons) and that the colour seen is the result of the remaining unabsorbed wavelengths or frequencies of light being reflected or transmitted. Only 20% of students scored all three marks. The equation needed was often incorrect with E = hcλ seen quite frequently. Many students failed to convert 490 nm to metres (or did so incorrectly). 03.2 proved to be a very discriminating question. Students should now be familiar with the fact that this paper contains a significant proportion of marks related to the description of practical scenarios. The key to success with such questions is to be familiar with a wide range of practical techniques and to be able to write concise, accurate descriptions. For example, in this case, a reference to plotting a graph of absorbance vs concentration needs to be preceded by a reference to taking a series of measurements of the absorbances for differing concentrations and it was not enough to simply repeat the question by saying ‘use the graph to find the unknown concentration’. The examiners wanted to see a description of how the graph should be used. It was encouraging to see many correct answers to 03.4 which proved to be one of the easiest questions on the paper
Text version
An aqueous transition-metal complex is coloured. Its absorption maximum is at wavelength 490 nm. A calibration graph is used to determine the iron concentration in a 250 cm^3 solution, found to be 4.66 x 10^-3 mol dm^-3. Use h = 6.63 x 10^-34 J s, c = 3.00 x 10^8 m s^-1 and Ar(Fe) = 55.8.
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AQA 7405 · November 2020 · Paper 3 · Q4 · 15 marks
15 marks
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In 04.1, as is often the case when a piece of syllabus recall is tested for the first time, relatively few students were able to recall the name of the process prevented by cisplatin during cell division. Students were expected to answer 04.2 by following the description in the question of a chloride ligand being replaced by a water molecule. In many cases students failed to appreciate that replacement of a negative chloride ion by a neutral water molecule would result in a net charge (of 1+) on the resulting complex. 04.3 proved to be very tricky for many students – perhaps due to the amount of reading needed to pick up on the clues in the question and to appreciate what was being asked. Students are clearly more familiar with questions asking them to show hydrogen bonding between base pairs because that is what many tried to do – and they ignored the need to include the complex in their diagram. Where the complex was included it was sometimes drawn as trans- rather than cis- and often without an indication that the bonds formed are co-ordinate bonds. The experiment in 04.4 was another example of a situation where a description of a (hopefully familiar) practical scenario was needed. Students found this very taxing and over half scored no marks. The question described measurements of concentration being taken at one-minute intervals and then asked for a description of graphical methods. Although there were several alternative possibilities, they all needed to start with a description of the need to plot a graph of these measured concentrations against time. The next stage needed to be some reference to a determination of rate from the concentration-time graph. When referring to a subsequent rate- concentration graph it is not enough to refer to a ‘straight line of constant gradient’ as that could also be a zero order line – a sketch graph was useful to some students here. The idea of constant half-lives is not on the syllabus, so this type of answer was not expected but was credited if seen. Most were able to complete the two simple calculator processes in 04.5 although some students seemed to try and arrive at the answers by using the successive differences between previous values in the table. However they failed to spot that the temperature differences were not all the same. Answers to 04.6 showed an improvement in graph skills with 70% of students scoring at least 3 marks. The negative scale confused some students and some forgot the need for at least 50% of the available space to be taken up by the plotted points. Most students then recognised that the gradient = Ea/R but some tried to solve the whole equation by inventing values for the ln terms. In some cases gradient calculations were the wrong way up or involved a misreading of the scales, e.g. 0.00341 was often seen as the value for ∆x instead of (0.00341 – 0.00310).
Text version
Cisplatin, cis-[Pt(NH3)2Cl2], is an anticancer drug. In aqueous solution it forms a species that bonds to adjacent guanine bases in DNA. Kinetic data for this process are analysed using concentration-time and Arrhenius plots.
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AQA 7405 · November 2020 · Paper 3 · Q5 · 8 marks
8 marks
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In 05.1 most students were able, at the least, to calculate the amount of hexane but some then got confused and attempted to use the more familiar q = mc∆T instead of the relevant equation given in the question. In some cases students erroneously converted the temperature change into Kelvin by adding 273. If temperature was incorrectly converted into Kelvin, in 05.2 it was marked as ‘ecf’ from 05.1 to avoid a double penalty for the same error. This enabled weaker students to score some marks. Most students seemingly failed to appreciate that question 05.3 was about why the value was not an ‘enthalpy change’ and, instead, offered answers that tried to explain why it was not a ‘standard’ change. Only 11% gained the mark. Students failed to recognise that, by definition, an enthalpy change is measured at constant pressure but the sealed nature of a bomb calorimeter will not allow expansion so the pressure will not remain constant. In 05.4, many students did not appreciate the need to double the thermometer uncertainty because two thermometer readings are taken.
Text version
A bomb calorimeter operates at fixed volume. Burning 2.00 g of hexane, Mr = 86.0, causes a temperature rise of 12.4 K. The magnitude of the molar heat change for hexane is 4154 kJ mol^-1. A second experiment burns 2.00 g of octane, Mr = 114.0, and gives a temperature rise of 12.2 K.
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AQA 7405 · November 2020 · Paper 3 · Q6 · 13 marks
13 marks
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In 06.1, many students just listed standard conditions without identifying the gas, solution or electrode. In 06.2, surprisingly, only about 9% of students were able to access Level 3, due mainly to a failure to address the indicative content in stage 1 ( preparation of the solution) despite the prompts in the question. Many of those who did try to calculate the mass of solid needed seemed to base the calculation on the 0.5 mol dm–3 value for the sulfuric acid instead of the required standard concentration of 1.0 mol dm–3. Students should also appreciate that weighing by difference is not the best approach when making up a solution of an exact concentration. The best method is to weigh the solid directly into the beaker before dissolving in a small volume of solvent and then transferring (with washings) to a volumetric flask. By contrast, many students covered all the items in stage 2 of the indicative content (how to set up the cell) where a diagram was often usefully employed. In 06.3, balancing the equation proved trickier than expected. The use of electrode potential data to explain the course of chemical reactions is always a challenge for students. 06.4 was not an exception and only 19% of students scored two or more marks. Many students failed to appreciate the need to discuss both comparisons and only focused on the interaction between copper and nitric acid. Many descriptions made confused references to the electrodes – often without referring to an electrode at all but using phrases such as ‘the E for nitric acid’. The best answers made clear references such as "Eo NO3–/NO > Eo Cu2+/Cu, so Cu can reduce NO3–". It was also often unclear what the students were suggesting as being oxidised or reduced – specific species need mentioning. Section B The percentage scores in the multiple-choice questions were overall much higher than in the written questions; the mean score across the 30 questions in Section B was 18.75 (62.5%). As always, there was a marked spread of difficulty across Section B. The vast majority of the questions yielded success rates of between 40 and 80%. The easiest questions were B17, B22 and B24 which had success rates in excess of 80%. Questions that students found particularly difficult, with a success rate of <40% were B7, B13 and B28.
Text version
Standard electrode potentials are used to investigate titanium and copper half-cells. The titanium half-cell is TiO^2+(aq), H+(aq) | Ti(s), and E = -0.88 V. The copper half-cell is Cu^2+(aq) | Cu(s), and E = +0.34 V. A standard TiO^2+ solution is prepared from TiOSO4, Mr = 159.9.
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AQA 7405 · June 2019 · Paper 1 · Q2 · 10 marks
10 marks
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[2.3] About half the students scored all the marks in part 3. Common errors included dividing by Avogadro’s number or dividing by 1000; some students could not rearrange the equation to find the mass of an ion, and some had difficulty in calculating the speed of the ion from the distance and time.
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Time-of-flight mass spectrometry of large molecules.
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AQA 7405 · June 2019 · Paper 1 · Q3 · 7 marks
7 marks
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[3.4] Amphoteric was well known, although the spelling was often incorrect.
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Periodicity and Period 4 chemistry.
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AQA 7405 · June 2019 · Paper 1 · Q5 · 13 marks
13 marks
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[5.1] Most students gave a correct equation in part 1 but the second mark was gained less frequently, with the role being defined incorrectly.
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Reactions and tests involving Group 7 compounds.
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AQA 7405 · June 2019 · Paper 1 · Q6 · 16 marks
16 marks
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[6.5] Students found this part challenging; most students did not recognise that the 3d sub-shell is full and therefore were unable to explain that d-d transitions are not possible and visible light is not absorbed.
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Copper-alloy iodometric titration and related copper/iodine chemistry.
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AQA 7405 · June 2019 · Paper 1 · Q7 · 10 marks
10 marks
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[7.4] Very few students could calculate the value of Kp, but the mark for the units was awarded more often.
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2SO3(g) <=> 2SO2(g)+O2(g).
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AQA 7405 · June 2019 · Paper 1 · Q8 · 11 marks
11 marks
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[8.1] Answers to part 1 were poor. Many students omitted all the lone pairs on the oxygen atoms or the necessary partial charges; only the more able students appreciated the linear nature of hydrogen bonds.
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Intermolecular bonding and shapes of POCl3 and ClF4-.
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AQA 7405 · June 2019 · Paper 1 · Q9 · 15 marks
15 marks
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[9.5] Only a very small number of students could give a correct mathematical expression.
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Water, weak-acid titration and buffers.
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AQA 7405 · June 2019 · Paper 2 · Q2 · 12 marks
12 marks
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[02.1] Most of this question was based on Required Practical Activity 5 example (a), from the Practical Handbook. Sadly, this experimental procedure did not seem familiar to many students and few completed the diagram correctly.
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Preparation and purification of cyclohexene from cyclohexanol.
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AQA 7405 · June 2019 · Paper 2 · Q3 · 9 marks
9 marks
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[03.2] Over half the students drew a correct structure but only a very small number could give its correct IUPAC name as buta-1,3-diene.
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Polyisoprene and stereoisomeric addition polymers used in golf balls.
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AQA 7405 · June 2019 · Paper 2 · Q4 · 6 marks
6 marks
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[04.3] Most students were able to calculate the rate constant, k, and to deduce its units correctly although others struggled to rearrange the rate equation.
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Initial-rate data and a fourth-order rate equation.
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AQA 7405 · June 2019 · Paper 2 · Q5 · 4 marks
4 marks
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Arrhenius constant calculation from a misprinted equation.
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AQA 7405 · June 2019 · Paper 2 · Q11 · 11 marks
11 marks
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[11.2] Part 2 was challenging and almost a quarter of students made no attempt to answer the question. The left hand (glycerol) part of the molecule was better known. Some students miscounted the carbon atoms in the acid part by including the methyl group of the biodiesel in the oil. Another common mistake was to draw the COO linkage the wrong way round.
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Esters, vegetable-oil biodiesel, stereochemistry, combustion and greenhouse warming.
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AQA 7405 · June 2019 · Paper 3 · Q3 · 17 marks
17 marks
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[3.4] A surprising number of students failed to score here, with a significant number of responses showing no concept of what was required, especially in the ‘conditions’ column. Of those students who made a reasonable attempt, there was some confusion about the significance of concentration with the [H+] in C needing to be 1.0 mol dm–3 so, if students chose H2SO4 its concentration needs to be 0.5 mol dm−3. Likewise for E it needed to be clear that the concentrations of Fe2+ and Fe3+ are both 1.0 mol dm−3, which caused problems for some students who chose to suggest the use of Fe2(SO4)3. For D it is clear that some students are using out of date concepts with references to 1 atm as standard pressure.
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A diagram shows a standard hydrogen electrode on the left connected by a U-shaped salt bridge and voltmeter to an Fe3+/Fe2+ half-cell with an inert electrode on the right. Labels are A salt bridge, B inert electrode, C acid solution, D hydrogen gas inlet and E Fe2+/Fe3+ solution. Later, Zn/Zn2+ and Cu2+/Cu cell data are analysed.
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AQA 7405 · June 2019 · Paper 3 · Q5 · 6 marks
6 marks
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[5.5] Most students knew both these pieces of measuring apparatus.
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A student determines the iron percentage in 680 mg of steel wire. All iron is converted to Fe2+, the solution is made to 100 cm^3, and 25.0 cm^3 portions are titrated with 0.0200 mol dm^-3 KMnO4. Titre results are 22.90, 22.70 and 22.60 cm^3.
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AQA 7405 · June 2018 · Paper 1 · Q1 · 6 marks
6 marks
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[01.1] Over 50% of students answered this part correctly, but some failed to gain maximum marks by omitting state symbols or electrons in the equations.
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Born-Haber cycle and lattice enthalpy of magnesium oxide.
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AQA 7405 · June 2018 · Paper 1 · Q2 · 9 marks
9 marks
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[02.2] Students answered this part well and most (70.8%) gave the correct expression; common errors included using square brackets, that denote concentration, or inverting the expression.
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Ammonia equilibrium, partial pressures and Kp.
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AQA 7405 · June 2018 · Paper 1 · Q3 · 11 marks
11 marks
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[03.1] Nearly all students (91.1%) gained both marks here.
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Entropy, Gibbs energy, heterogeneous catalysis and ammonia oxidation.
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AQA 7405 · June 2018 · Paper 1 · Q5 · 15 marks
15 marks
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[05.3] 81.8% of students gave the correct reason here.
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Strong acids, pH, Kw, buffers and Period 3 oxides.
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AQA 7405 · June 2018 · Paper 1 · Q6 · 6 marks
6 marks
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[06.1] Although 73.4% of students were able to answer correctly, some stated that the circuit was completed by the flow of electrons.
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A copper concentration cell and its changing EMF.
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AQA 7405 · June 2018 · Paper 1 · Q9 · 7 marks
7 marks
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Vanadium Compounds and Ions
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Vanadium redox potentials, complexes, decomposition and catalysis.
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AQA 7405 · June 2018 · Paper 1 · Q10 · 7 marks
7 marks
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[10.1] This challenging question discriminated very well, with 16.6% of students scoring all of the marks and 20% scoring zero marks; 5.7% did not attempt this question. Many students calculated the amount, in moles, of hydrochloric acid added and the amount of sodium hydroxide used in the titration. Many did not then multiply the amount of sodium hydroxide by 10 to calculate the total amount, in moles, of hydrochloric acid remaining and fewer students still were able to calculate the original amount of sodium carbonate. Many students could convert mg to g. Only the best students could continue to the end and calculate that x = 1.
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Back titration to find waters of crystallisation in hydrated sodium carbonate.
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AQA 7405 · June 2017 · Paper 1 · Q1 · 8 marks
8 marks
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[01.3] Many students understood that the lattice was not perfectly ionic and had some covalent character. Linking the covalent character with stronger bonding eluded all but the strongest students.
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Silver iodide lattice enthalpy, bonding and iodide testing.
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AQA 7405 · June 2017 · Paper 1 · Q2 · 9 marks
9 marks
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[02.2] Although 34.4% of students scored full marks, the question differentiated well overall. Common errors involved either failure to add/subtract the correct amount in moles of sodium hydroxide or to add/subtract the wrong way round.
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Ethanoic-acid/ethanoate buffer calculations.
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AQA 7405 · June 2017 · Paper 1 · Q4 · 8 marks
8 marks
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[04.2] Most students gave the correct equation, but some used the wrong state symbols or omitted them. The identity of the isotope was well known but some students lost a mark by using the symbol for the atom rather than the m/z value.
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Titanium isotope mass spectrum and TOF calculations.
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AQA 7405 · June 2017 · Paper 1 · Q5 · 6 marks
6 marks
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Most students calculated ΔS correctly and gave the correct expression for ΔG. Many students then went on to calculate the value of ΔG correctly. Some students failed to convert the temperature to a value in kelvin, some failed to convert the energy into kilojoules, and some did not give the value of ΔG to the required precision.
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Entropy and Gibbs feasibility of TiCl4 manufacture.
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AQA 7405 · June 2017 · Paper 1 · Q6 · 13 marks
13 marks
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[06.3] Most students answered this well, but “simple covalent” was a common incorrect, incomplete answer for sulfur dioxide.
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Period 3 elements, oxides, structures and acid-base reactions.
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AQA 7405 · June 2017 · Paper 1 · Q7 · 9 marks
9 marks
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[07.6] Students could often state that the electronic configuration was d10, but the effect on electron transitions was less well known. Students often failed to realise the importance of visible light being absorbed. Some students scored the mark by stating the complex was colourless.
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Aqueous copper complexes and ligand substitution.
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AQA 7405 · June 2017 · Paper 1 · Q9 · 14 marks
14 marks
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[09.2] Only a few students did not understand what was being asked for; most errors were either arithmetic errors or rounding errors.
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Industrial methanol equilibria from methane and synthesis gas. Official Figure 1 (constant pressure), approximate plotted coordinates (temperature / C, methane conversion / %): (600,15), (650,25), (700,40), (750,60), (800,85), (850,95), (900,95). Official Figure 2 (constant temperature), approximate plotted coordinates (pressure / kPa, methane conversion / %): (1000,80), (2000,65), (3000,56), (4000,51), (5000,49).
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AQA 7405 · June 2017 · Paper 1 · Q11 · 14 marks
14 marks
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[11.3] Many students struggled to draw the displayed formula; those who got close often omitted the carbon atoms from the ligand. Most students knew the bond angle, but some incorrectly gave 120° or 109.5°. The most common incorrect type of isomerism given was stereoisomerism or cis/trans.
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Ethanedioate mixture titrations and an iron(III) ethanedioate complex.
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AQA 7405 · June 2017 · Paper 2 · Q1 · 13 marks
13 marks
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[01.5] Both the reagent (which must be a complete compound) and a condition were needed to score the mark; several omitted the condition.
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Reactions of 1-bromopropane.
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AQA 7405 · June 2017 · Paper 2 · Q2 · 4 marks
4 marks
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[02.1] Most students were able to draw a suitable tangent, although some drew a very small tangent which made calculating a gradient from it more difficult and less precise.
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Initial-rate graph and rate equation rate=k[A]^2[B].
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AQA 7405 · June 2017 · Paper 2 · Q3 · 7 marks
7 marks
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[03.1] This kinetics question was answered well apart from occasional slips in deducing the units.
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Rate constant and Arrhenius activation energy.
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AQA 7405 · June 2017 · Paper 3 · Q4 · 9 marks
9 marks
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[04.4] The provision of alternative data ensured that students who had difficulty with question 04.3 were not disadvantaged here and over 50% gained full marks. Data in the stem were again crucial here.
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Weak-acid/strong-base titration of HX with sodium hydroxide.
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AQA 7405 · sample1 · Paper 3 · Q5 · 6 marks
6 marks
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Mass spectra of ethanedioic-acid esters.
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June 20255 questions

Paper 2 · Q414 marks · Calculator · multi · standard3.1.2 Amount of substanceView question in paper (p.12)
Paper 2 · Q712 marks · Calculator · multi · hard3.1.2 Amount of substanceView question in paper (p.21)Mark scheme (p.28)
Paper 3 · Q19 marks · Calculator · multi · standard3.1.4 Energetics · 3.1.8 Thermodynamics (A-level only)View question in paper (p.2)Mark scheme (p.11)
Paper 3 · Q215 marks · Calculator · multi · hard3.1.9 Rate equations (A-level only)View question in paper (p.6)Mark scheme (p.13)
Paper 3 · Q7-3630 marks · Calculator · multi · standard3.1.1 Atomic structure · 3.1.3 Bonding · 3.1.5 Kinetics

June 20244 questions

Paper 1: Q1 (p.2, 13 marks), Q7 (p.23, 8 marks)

Paper 2: Q2 (p.3, 8 marks)

Paper 3: Q6-35 (30 marks)

June 20233 questions

Paper 3: Q1 (p.2, 17 marks), Q5 (p.14, 10 marks), Q7-36 (30 marks)

June 20225 questions

Paper 1: Q2 (p.6, 12 marks), Q4 (p.14, 16 marks), Q5 (p.17, 15 marks)

Paper 3: Q1 (p.3, 18 marks), Q6-35 (30 marks)

November 20214 questions

Paper 2: Q3 (p.10, 7 marks)

Paper 3: Q1 (p.2, 20 marks), Q3 (p.10, 11 marks), Q07-36 (30 marks)

November 20203 questions

Paper 2: Q5 (p.10, 9 marks)

Paper 3: Q1 (p.2, 8 marks), Q7-36 (30 marks)

June 20197 questions

Paper 1: Q1 (p.2, 9 marks)

Paper 2: Q7 (p.16, 7 marks), Q8 (p.18, 10 marks), Q10 (p.24, 10 marks)

Paper 3: Q1 (p.2, 13 marks), Q2 (p.6, 15 marks), Q6-35 (30 marks)

June 201810 questions

Paper 1: Q4 (p.9, 18 marks), Q8 (p.20, 17 marks)

Paper 2: Q3 (p.6, 16 marks), Q4 (p.10, 13 marks), Q5 (p.11, 14 marks)

Paper 3: Q1 (p.2, 19 marks), Q2 (p.8, 12 marks), Q3 (p.10, 13 marks), Q4 (p.14, 16 marks), Q05-34 (30 marks)

June 20177 questions

Paper 1: Q3 (p.6, 9 marks), Q10 (p.21, 9 marks)

Paper 2: Q5 (p.10, 9 marks), Q10 (p.20, 21 marks)

Paper 3: Q1 (p.2, 14 marks), Q3 (p.9, 18 marks), Q5-34 (30 marks)

sample118 questions

Paper 1: Q1 (p.3, 10 marks), Q2 (p.4, 7 marks), Q3 (p.7, 6 marks), Q4 (p.8, 16 marks), Q5 (p.12, 10 marks), Q6 (p.14, 12 marks), Q7 (p.18, 11 marks), Q8 (p.22, 11 marks), Q9 (p.24, 12 marks)

Paper 2: Q1 (p.2, 12 marks), Q2 (p.6, 6 marks), Q3 (p.8, 12 marks), Q5 (p.14, 5 marks), Q9 (p.22, 18 marks)

Paper 3: Q1 (p.2, 16 marks), Q2 (p.5, 13 marks), Q4 (p.8, 15 marks), Q6-35 (30 marks)

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