Chemical changes questions

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• AQA 8462 · June 2025 · Paper 1F · Q2 · 6 marks

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  [02.6] Fewer than half of responses gave the correct answer, with more than half believing that temperature decreases in an exothermic reaction.

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  Metals react with acids to produce a salt and a gas. A student investigated the temperature change when 1 g of each of several metals was added to 25 cm³ of hydrochloric acid initially at 20 °C.

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• AQA 8462 · June 2025 · Paper 1F · Q3 · 8 marks

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  [03.1] Two thirds of students were able to identify sodium chloride solution as the only possible electrolyte. Water was the more popular distractor, but a surprising number chose solid potassium bromide.

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  Cells contain chemicals that react to produce electricity. A cell used one fixed copper electrode and one metal electrode, both in an electrolyte. The measured voltages were: A 1.1 V, B 0.0 V, C 0.8 V, D 2.7 V.

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• AQA 8462 · June 2025 · Paper 1F · Q4 · 10 marks

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  [04.4] Only two fifths of students realised that the acid should be added dropwise and / or that the solution should be swirled. One popular misconception was that the addition should be timed. Stirring was not accepted as an alternative to swirling, but adding the acid slowly was accepted as an alternative to dropwise or drop by drop. © 2025 AQA

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  A student found the volume of acid that neutralised 25.0 cm³ of alkali. They measured the alkali into a conical flask, added a few drops of substance X, placed the flask on a white tile, added acid until a colour change, measured the acid volume, and repeated three times.

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• AQA 8462 · June 2025 · Paper 1F · Q5 · 9 marks

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  [05.6] Three quarters of students gave the correct value, with 2.7 cm3 being the more popular distractor.

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  This question is about electrolysis. Aluminium is extracted by electrolysis of a molten mixture of aluminium oxide and cryolite; the products are molten aluminium and oxygen gas. A student also investigated electrolysis of magnesium sulfate solution at currents of 0.05 A and 0.10 A.

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• AQA 8462 · June 2025 · Paper 1F · Q7 · 8 marks

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  [07.3] Four fifths of students scored both marks. A few inverted the expression provided.

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  This question is about mixtures. A mixture contains salt, which is soluble in water, and sand, which is insoluble in water.

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• AQA 8462 · June 2025 · Paper 1F · Q10 · 11 marks

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  [10.3] Whilst a third of students scored one mark, only about one in ten scored all three. Many could not recall the expression for percentage atom economy and therefore did not attempt to find the total Mr of the reactants. A significant minority added the two relative atomic masses provided to give 124 and then divided by 128. © 2025 AQA

  Text version

  This question is about metals and metal oxides. Tin is extracted by SnO₂ + C -> Sn + CO₂. Cadmium is extracted by CdO + C -> Cd + CO. Tungsten oxide reacts by WO₃ + 3H₂ -> W + 3H₂O.

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• AQA 8462 · June 2025 · Paper 1H · Q3 · 11 marks

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  [03.3] More than two thirds of students achieved full marks. Some did not calculate a total Mr but used the Mr of CdO instead; these answers were not creditworthy. Others added up all the Mr of reactants and products instead of just the reactants; these gained partial credit.

  Text version

  This question is about metals and metal oxides. Tin is extracted by SnO₂ + C -> Sn + CO₂. Cadmium is extracted by CdO + C -> Cd + CO. Tungsten oxide reacts by WO₃ + 3H₂ -> W + 3H₂O.

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• AQA 8462 · June 2025 · Paper 1H · Q6 · 11 marks

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  [06.2] Only a half of students knew that cryolite was the correct substance. The most common incorrect answer was water.

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  Aluminium is extracted by electrolysis of molten aluminium oxide mixed with another substance. Oxygen forms at the positive electrode.

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• AQA 8462 · June 2025 · Paper 1H · Q8 · 12 marks

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  [08.3] The vast majority gave the correct reading. The most common error was 25.3 cm3.

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  This question is about alkalis and acids. A student planned to titrate 25.0 cm³ of known sulfuric acid against sodium hydroxide using universal indicator, a pipette, conical flask, white tile and burette, adding alkali while swirling until a colour change and repeating to consistency.

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• AQA 8462 · June 2025 · Paper 1H · Q9 · 11 marks

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  [09.2] Nearly a half of students gained full marks in this calculation and over three quarters could make some progress. This was a multi-step calculation, which is classed as an extended response question. As such, the working has to make sense chemically. Those students who managed to put the data together in such a way as to obtain an answer of 78.9%, but whose working made no sense chemically, were often limited to the mark for the correct number of significant figures. There were many excellent fully correct answers, and many students were able to make some progress by calculating the number of moles of iodine and / or zinc iodide. While most adopted the expected approach, calculating the expected mass of zinc iodide and finding the actual mass as a percentage of that value, two other valid approaches also gained credit. One of these was to find the moles of zinc iodide produced as a percentage of the expected moles. The other, far less commonly seen, was to find the mass of iodine actually reacted and take that as a percentage of the mass provided. Of those who adopted the approach of calculating the expected mass of zinc iodide, many surprisingly calculated the mass of zinc and added that to the mass of iodine, rather than simply multiplying the number of moles by the Mr of ZnI2, which was provided. Students had little difficulty in rounding correctly to 3 significant figures.

  Text version

  Zinc reacts with iodine to produce zinc iodide in ethanol. Ethanol is flammable and boils at 78 °C. Zinc is insoluble in ethanol; iodine and zinc iodide are soluble.

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• AQA 8462 · June 2024 · Paper 1F · Q2 · 6 marks

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  [02.7] Students found this standard demand question difficult. Just over a third of students identified the formula of barium chloride, but the distractor Ba2Cl was even more popular.

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  A titration measures the volumes of an acid and an alkali that neutralise each other. Acid is added from a burette to alkali in a conical flask until the solution is neutralised.

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• AQA 8462 · June 2024 · Paper 1F · Q3 · 9 marks

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  [03.8] Students struggled with this standard demand question, with only a quarter gaining a mark. More than a half of students selected the second distractor, in which both parts of the statement are the opposite of the correct version. When temperature decreases, heat energy is being taken in from the surroundings and converted to chemical energy, so the reaction is endothermic. It is this reduction in heat energy that causes the temperature decrease. A misconception for many students is thinking that when heat energy is taken in from the surroundings it remains as heat energy in the system, causing the confusion with the direction of temperature change.

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  Zinc reacts with copper sulfate solution: zinc + copper sulfate -> zinc sulfate + copper. A student measured energy changes using 25 cm³ of copper sulfate solution in a polystyrene cup and different masses of zinc powder.

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• AQA 8462 · June 2024 · Paper 1F · Q6 · 10 marks

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  [06.1] Fewer than a half of students identified the reason why molten substances can be electrolysed. The incorrect distractor that electrons can move through the substance was almost as popular.

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  This question is about electrolysis and extracting metals. The reactivity sequence supplied is potassium, lithium, carbon, zinc, tin, gold, in decreasing reactivity.

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• AQA 8462 · June 2024 · Paper 1F · Q7 · 8 marks

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  [07.2] Two thirds of students identified sodium chloride solution as the correct substance to be an electrolyte. The two distractors, pure water and solid lead bromide, were equally popular.

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  This question is about chemical cells. Figure 14 shows a cell with Metal A and Metal B in an electrolyte, with both metal electrodes connected to a voltmeter.

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• AQA 8462 · June 2024 · Paper 1F · Q8 · 10 marks

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  [08.2] About a half of students gave a correct observation that would show that the reaction was no longer proceeding. Many did not realise that they were looking for signs of the reaction having stopped, and gave observations they would make while it was still ongoing.

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  A student produced a salt by reacting excess copper carbonate with 50 cm³ of sulfuric acid, filtering, warming the filtrate until crystals started to appear, then cooling to crystallise.

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• AQA 8462 · June 2024 · Paper 1F · Q9 · 8 marks

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  [09.2] More than a third of students could give two correct observations, and more than four fifths could give one, with bubbling, floating and a flame being the most popular. ‘Gas produced’ did not gain credit as it is not an observation but a deduction from the observation of bubbling. ‘Fizzing’ is taken to mean effervescence, so fizzing and bubbling are the same thing rather than two different observations. Credit was not given for any observation requiring extra equipment such as a thermometer or an indicator.

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  This question is about the periodic table. Sodium and potassium are in Group 1. Group 7 elements are halogens.

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• AQA 8462 · June 2024 · Paper 1H · Q1 · 10 marks

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  [01.5] The great majority of students were able to substitute the values and rearrange the expression to give the correct answer. Some students used their calculator incorrectly, using both the % button and also dividing by 100, giving an answer that was a factor of 100 too low. They seemed unfamiliar with the idea that the symbol ‘%’ means divided by 100. A minority of students tried to incorporate the 50 cm3 into their calculation.

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  A student produced a salt by reacting excess copper carbonate with 50 cm³ of sulfuric acid, filtering, warming the filtrate until crystals started to appear, then cooling to crystallise.

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• AQA 8462 · June 2024 · Paper 1H · Q2 · 8 marks

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  [02.6] Three quarters of students identified the correct pair of solutions, with the spread of incorrect responses being approximately equal.

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  This question is about the periodic table. Sodium and potassium are in Group 1. Group 7 elements are halogens.

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• AQA 8462 · June 2024 · Paper 1H · Q4 · 8 marks

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  [04.2] This question discriminated well, with a quarter of students scoring 3 or 4 marks and the great majority scoring at least one mark. The question asked students to explain the results, but many simply described them. It was not sufficient just to describe the temperature increasing with the addition of more zinc; reference to the reaction being exothermic was also needed. The fact that the maximum temperature change occurred when 0.80 g of zinc was added was the mark scored most often, but many students were also able to explain this turning point in terms of no further reaction being possible because the zinc was now in excess. There were some excellent answers in terms of the zinc being the limiting reactant up to 0.8 g, after which the copper sulfate became the limiting reactant.

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  A student investigated the energy change when different masses of zinc powder reacted with 25 cm³ of copper sulfate solution in a polystyrene cup. A second student repeated the method four times using 0.50 g of zinc.

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• AQA 8462 · June 2024 · Paper 1H · Q5 · 7 marks

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  [05.3] Fewer than half of the students knew that hydrogen was the product. Calcium was the most popular incorrect response, with chlorine and hydrogen ions also being named as the product.

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  This question is about ionic compounds and electrolysis. Calcium chloride is ionic. Aqueous calcium chloride and green copper chromate solution can be electrolysed.

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• AQA 8462 · June 2024 · Paper 1H · Q6 · 11 marks

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  [06.1] Over three fifths of students scored all three marks. Most students could list the metals in order of decreasing reactivity, although some ignored the sign and ordered the metals in order of absolute magnitude of voltage. A few tried to remember the reactivity series, even though nickel and silver are not listed in the specification. The best answers justified the order not only in terms of the most reactive metal producing the most positive voltage, but also that the negative voltages were produced by elements less reactive than nickel.

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  Figure 6 shows a chemical cell with a nickel electrode and electrode A in 1.0 mol/dm³ sodium chloride, both connected to a voltmeter. Results for electrode A were: Cu -0.59 V; Mg 2.12 V; Ni 0.00 V; Ag -1.05 V; Zn 0.51 V.

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• AQA 8462 · June 2024 · Paper 1H · Q7 · 15 marks

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  [07.2] This question discriminated well, with over a half of students scoring 2 or 3 marks. There were many well-expressed, complete answers. Common errors often involved an attempt to describe some sort of stronger bonding (sometimes covalent or ionic) in the alloy. Some lost credit because of poor use of language; it is not ‘metals’ which are different sizes, but their atoms (or positive ions). A common error was to refer to different shapes of atoms. ‘Particles’ is also insufficient as it could refer to other types of particle than atoms. ‘Intermolecular forces’ were often referred to, although they are not present in either a pure metal or an alloy.

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  This question is about iron. The common oxides include Fe₂O₃ and Fe₃O₄.

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• AQA 8462 · June 2024 · Paper 1H · Q9 · 12 marks

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  [09.1] Over a half of students knew that a weak acid is one which is partially ionised, although many forgot to state that this was in aqueous solution. Some students incorrectly stated that an acid is ionising (ionises other species) rather than ionised (is itself ionised). Some incorrectly stated that it was H+ ions which are ionised or dissociated, rather than the acid molecules. The H+ ions are the result of the ionisation or dissociation.

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  This question is about acids and their reactions.

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• AQA 8462 · June 2023 · Paper 1F · Q2 · 10 marks

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  [02.4] This was well answered, with the vast majority recognising a burette as the correct piece of equipment.

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  This question is about acids, alkalis and titration. A student titrated 25.0 cm³ sodium hydroxide solution with hydrochloric acid. Four acid volumes were 24.3, 24.5, 28.1 and 24.4 cm³.

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• AQA 8462 · June 2023 · Paper 1F · Q6 · 9 marks

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  [06.2] The great majority scored at least one mark. Students were asked for observations which could be seen, so those which could be heard did not gain credit. Bubbling and fizzing are the same observation; many gave both terms and no other observation so scored only one mark. Some incorrectly said that the water changes colour (possibly because they have seen the reaction carried out in the presence of an indicator).

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  This question is about metals. Platinum is used for jewellery; sodium reacts with water. Copper is a transition element and sodium is in Group 1. Aluminium and copper can both make cooking pans.

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• AQA 8462 · June 2023 · Paper 1F · Q7 · 6 marks

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  [07.1] This question was answered by fewer than half of the students showing that many students do not read the entire question, but focus only on the sentence above an answer line. As there was no answer line, the instruction to complete Figure 8 was missed. Of those who did respond, most scored at least one mark. Most of those who did answer realised that two of each ion should be drawn, but many placed the ions directly under the same type of ion, instead of in the alternate positions.

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  This question is about ionic compounds and electrolysis. Sodium chloride is ionic. Aluminium is extracted from a molten aluminium oxide/cryolite mixture. Electrolysis of aqueous sodium sulfate produces hydrogen and oxygen.

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• AQA 8462 · June 2023 · Paper 1F · Q8 · 10 marks

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  [08.4] This question also discriminated well. Most students could substitute the values correctly into the given expression. However, some did not know how to evaluate that expression and some incorrectly rounded a value of 77.9% to 77% instead of 78%.

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  Iron oxide is displaced by carbon. Copper oxide reacts with hydrogen: CuO + H₂ -> Cu + H₂O. A student also tested metals A-D in each metal-sulfate solution. Results (columns A/B/C/D sulfate) were A: no/no/yes/no; B: yes/no/yes/no; C: no/no/no/no; D: yes/yes/yes/no.

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• AQA 8462 · June 2023 · Paper 1F · Q11 · 8 marks

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  [11.2] Few students gave two correct answers, although over a third could suggest one, zinc being the most common correct answer. Nearly a fifth of students did not give an answer.

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  This question is about making soluble salts.

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• AQA 8462 · June 2023 · Paper 1H · Q3 · 8 marks

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  [03.1] This question discriminated very well, with nearly two fifths of students giving a Level 3 answer, another third reaching Level 2, and nearly all of the others reaching Level 1. Many students gave excellent descriptions of the salt preparation, although many did not state which acid would be used in order to obtain zinc chloride. Some students only described the crystallisation process, leaving out essential steps such as starting with the acid, adding excess of the zinc carbonate, and filtering out the excess. A few would not have made crystals because they evaporated to dryness by heating. Many students appear to believe that the acid is being evaporated off the solution, rather than water. There were infrequent references to using a water bath of an electric heater for the evaporation; use of a Bunsen burner directly is likely to lead to heating to dryness. A few students seem to think that every practical activity is an investigation, trying inappropriately to name independent, dependent and control variables.

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  This question is about making a soluble salt.

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• AQA 8462 · June 2023 · Paper 1H · Q5 · 12 marks

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  [05.4] About three fifths of students knew that the OH– ion is responsible. When asked for a formula, an equation is not an appropriate response.

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  This question is about acids and alkalis.

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• AQA 8462 · June 2023 · Paper 1H · Q6 · 9 marks

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  [06.3] Nearly a third of students scored at least one mark on this high demand question, which required the linking of two different areas of the specification. Students needed to link what they knew about alloys (distorted layers due to different sized atoms) to electrical conductivity, to suggest that the distorted layers would impede the flow of electrons. Some students seem to think that the atoms in an alloy have different shapes.

  Text version

  This question is about uses of metals in electrical wires. Electrical wires can be made from: aluminium, copper, silver. Figure 6 shows three uses of electrical wires: overhead power cables, wiring in homes, and printed circuit boards. Table 5 shows information about the metals (the higher the value for electrical conductivity, the better the metal is at conducting electricity): electrical conductivity in arbitrary units — aluminium 37.7, copper 59.6, silver 63.0; density in g/cm³ — aluminium 2.7, copper 9.0, silver 10.5; cost of metal per kg in £ — aluminium 1.50, copper 7.00, silver 640.00.

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• AQA 8462 · June 2023 · Paper 1H · Q7 · 9 marks

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  [07.4] Nearly two thirds of students scored at least one mark, but just over half of these also scored the second mark. The easiest change to the apparatus is to change the test tubes to measuring cylinders or inverted burettes. Many students suggested gas syringes; this was allowed, although it would be difficult to set up the apparatus in such a way that this would work. However, a ‘gas cylinder’ is not a measuring device. One popular misconception is that gas would escape from the apparatus so a lid should be used. Most students realised that the reason was so that the gas volume could be measured rather than estimated, or that test tubes have no scale; any equivalent way of expressing this idea was allowed. Some students used imprecise language such as ‘so the gas could be measured’ without referring to volume or a scale.

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  This question is about electrolysis. Aluminium is manufactured by electrolysing a molten mixture of aluminium oxide (Al₂O₃) and cryolite (Na₃AlF₆).

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• AQA 8462 · June 2023 · Paper 1H · Q8 · 10 marks

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  [08.2] About three fifths of students were able to give a correct formula by analogy with ammonia. PH2 was a common incorrect response.

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  This question is about elements in the periodic table.

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• AQA 8462 · June 2022 · Paper 1F · Q2 · 6 marks

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  [02.2] About 60% of students correctly identified diagram A as a mixture of compounds. D, a pure compound, was the most popular incorrect response .

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  This question is about elements, compounds and mixtures. Four liquids A-D have boiling points 97, 138, 78 and 118 °C respectively and are separated by fractional distillation.

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• AQA 8462 · June 2022 · Paper 1F · Q3 · 5 marks

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  [03.2] This question was answered correctly by nearly all students.

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  This question is about acids. Universal-indicator colours available are blue, green, purple, red and yellow. A student also titrates an acid with an alkali.

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• AQA 8462 · June 2022 · Paper 1F · Q5 · 6 marks

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  [05.7] Nearly all students were able to give the correct relationship.

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  A student investigated magnesium ribbon reacting with hydrochloric acid, collecting gas in a gas syringe. The student used different ribbon lengths and repeated each four times. For one length the gas volumes were 19, 36, 37 and 32 cm³. Mean volumes for lengths 10, 20, 30, 40, 50 and 60 mm were 7, 14, 21, 28, 35 and 42 cm³.

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• AQA 8462 · June 2022 · Paper 1F · Q6 · 5 marks

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  [06.5] Just over half of the students could count the atoms in the figure and then write the formula correctly. Many failed to gain credit because the numbers were not subscripts but the same size as the letters, or even larger.

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  This question is about carbon and its compounds. Diamond has a giant covalent structure. Carbonic acid has formula H₂CO₃.

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• AQA 8462 · June 2022 · Paper 1F · Q8 · 8 marks

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  [08.4] This was well answered, with the great majority of students naming both correct products.

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  A student electrolyses sodium sulfate solution containing hydrogen, hydroxide, sodium and sulfate ions. Oxygen forms at the positive electrode. Molten electrolysis products include potassium iodide -> potassium + [blank], and zinc bromide -> [blank] + bromine. Titanium is produced by TiO₂ -> Ti + O₂.

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• AQA 8462 · June 2022 · Paper 1H · Q4 · 7 marks

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  [04.2] Few students gained this mark. Many students said the reason was to use up all the acid, without considering why that was necessary - answers in terms of ease of removal of the excess reactant were required. Whilst students seem very familiar with the method for making a salt, they appear to be less familiar with the reasons for each step.

  Text version

  Zinc oxide reacts with hydrochloric acid: ZnO(s)+2HCl(aq) -> ZnCl₂(aq)+H₂O(l). Zinc also displaces copper: Zn+CuCl₂ -> ZnCl₂+Cu.

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• AQA 8462 · June 2022 · Paper 1H · Q5 · 11 marks

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  [05.1] Nearly half of students described how a specific observation would differ. Vague comments about a more violent reaction, with no specific visual observation, did not gain credit.

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  Rubidium is below potassium in Group 1. Neon isotope data: mass 20 at 90.48%, mass 21 at 0.27%, mass 22 at 9.25%.

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• AQA 8462 · June 2022 · Paper 1H · Q6 · 9 marks

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  [06.2] Most students realised the need to prevent the products from reacting together and reforming sodium chloride. However, a significant minority failed to appreciate that the reverse reaction would occur and instead focused on preventing the products from mixing or ensuring product purity.

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  Molten sodium chloride is electrolysed industrially to make sodium, with a mesh keeping products apart. Electrolysis of aqueous sodium chloride makes two gases and an alkaline solution.

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• AQA 8462 · June 2022 · Paper 1H · Q7 · 14 marks

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  [07.1] This was well answered, with more than half of students scoring both marks. There was, however, some ambiguous use of the word ‘it’ such as ‘it shows that it is below carbon because it displaces it’. If it was not clear what ‘it’ referred to, credit was not given.

  Text version

  Silicon can be extracted by 2C+SiO₂ -> Si+2CO or by 2Mg+SiO₂ -> Si+2MgO. Si₂H₆ reacts: 2Si₂H₆(g)+7O₂(g) -> 4SiO₂(s)+6H₂O(g).

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• AQA 8462 · June 2022 · Paper 1H · Q8 · 14 marks

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  [08.2] Most students were able to explain that the first titration is anomalous and the mean of the other four titrations is used. Some correctly described this as taking the mean of the concordant results, or the mean of the results within 0.10 cm3. Incorrect answers included that the value used was the mean of all five results, or that it was the mode or median of the results.

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  A student titrated 25.00 cm³ hydrochloric acid with 0.100 mol/dm³ barium hydroxide. Volumes were 23.90, 23.45, 23.55, 23.55 and 23.45 cm³; the calculation used 23.50 cm³. Equations: 2HCl+Ba(OH)₂ -> BaCl₂+2H₂O; H₂SO₄+Ba(OH)₂ -> BaSO₄(s)+2H₂O.

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• AQA 8462 · November 2021 · Paper 1F · Q3 · 9 marks

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  This question is about Group 1 elements and the formation of sodium fluoride. Sodium has electronic structure 2,8,1 and potassium has 19 electrons.

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• AQA 8462 · November 2021 · Paper 1F · Q4 · 9 marks

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  A student reacted cobalt, magnesium and zinc powders with 50 cm3 hydrochloric acid. Temperature increases (degC) were cobalt 6,7,5,9; magnesium 54,50,37,55; zinc 18,16,18,20. The anomalous magnesium result is 37.

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• AQA 8462 · November 2021 · Paper 1F · Q6 · 4 marks

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  Copper carbonate reacts with an acid to produce copper chloride and a gas. A pure dry sample of copper chloride is made by adding excess carbonate, filtering, gently heating the solution until crystals form, cooling, rinsing and drying.

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• AQA 8462 · November 2021 · Paper 1F · Q7 · 7 marks

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  Students electrolysed aqueous salt solutions and molten ionic compounds. Copper sulfate gives copper at the negative electrode; sodium chloride gives hydrogen there. Molten zinc chloride and potassium iodide are also considered.

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• AQA 8462 · November 2021 · Paper 1F · Q10 · 10 marks

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  Element R is extracted by 3H₂+RO₃ -> R+3H₂O; the total M_r of reactants is 150. Tin is extracted by SnO₂+C -> Sn+CO₂. A_r: H=1, C=12, O=16, Sn=119. Three tungsten-extraction methods use carbon (low cost; W, CO2 and tungsten carbide), hydrogen (high cost; W and water vapour), or iron (low cost; W and iron oxide); other solids must be separated.

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• AQA 8462 · November 2021 · Paper 1H · Q3 · 10 marks

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  [03.2] This was well answered. Credit was given to those who applied an incorrect response to question 03.1 correctly. Some students gave an answer which corresponded to their answer to question 03.1 used as atomic number rather than relative atomic mass.

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  Element R is extracted by 3H₂+RO₃ -> R+3H₂O; total reactant M_r=150. Tin extraction is SnO₂+C -> Sn+CO₂. A_r: H=1, C=12, O=16, Sn=119. Tungsten methods use carbon (low cost; W, CO2, tungsten carbide), hydrogen (high cost; W, water vapour), or iron (low cost; W, iron oxide).

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• AQA 8462 · November 2021 · Paper 1H · Q4 · 12 marks

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  [04.4] The electron arrangements of both atoms and ions were required for full marks, as well as the ratio of sodium ions to oxide ions and the correct charges on the ions. Few students scored all the marks as they did not draw the atoms of sodium and oxygen before reaction. Many tried to draw covalent structures. The ratio of 2 atoms of sodium to one of oxygen was well known. Students should be aware that electrons cannot be in two places at the same time and should not be drawn as if they are. Some students drew both ionic and covalent structures, thereby contradicting themselves and losing the marks for a correct ionic structure. A great deal of time and effort would be saved by drawing the outer electrons only, as in the specification.

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  This question is about Group 1 and sodium oxide.

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• AQA 8462 · November 2021 · Paper 1H · Q5 · 10 marks

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  [05.5] Very few students knew that a water bath or an electric heater should be used, despite this being stated in the specification.

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  This question is about making salts, including magnesium sulfate crystals and iron(III) chloride.

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• AQA 8462 · November 2021 · Paper 1H · Q6 · 8 marks

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  [06.3] Students were expected to do a simple comparison of the temperature change when each metal was added separately to silver nitrate solution. A control variable was needed for full marks to be awarded, as well as how the results would show which metal was the more reactive. Some students did not appear to know how to progress, with some trying to measure a temperature change while heating with a Bunsen burner, and some appearing to confuse reactivity with melting or boiling point. Of those students who did realise what was required, many spoiled their control variable by referring to the same ‘amount’ of a substance instead of volume, or concentration, or mass, as appropriate to the substance. Many students referred to temperature rather than temperature change. A few students tried to get round the fact that no other chemicals were available by making zinc nitrate and then seeing if Q would react with it. This approach could have worked but only if they had taken steps to ensure that all the silver nitrate had reacted before adding Q.

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  Substances A-D have: A mp -117 degC, bp 79 degC, non-conductor solid/liquid; B 801/1413, non-conductor solid, conductor liquid; C 1535/2750, conductor solid/liquid; D 1610/2230, non-conductor solid/liquid. Metal Q and zinc are both more reactive than silver.

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• AQA 8462 · November 2021 · Paper 1H · Q7 · 16 marks

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  [07.2] Many students were unable to write the formula of bromine. Those who could, often scored at least one mark, although the half-equation was not always balanced.

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  This question compares electrolysis with chemical cells and investigates copper nitrate electrolysis. At 20 minutes, Figure 5 shows 0.12 g copper at 0.3 A and 0.24 g at 0.6 A.

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• AQA 8462 · November 2021 · Paper 1H · Q9 · 9 marks

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  [09.4] As with other calculations, students often failed to explain what they were doing, which made it difficult for the examiners to award partial credit. Numbers were scattered around without helpful words such as ‘moles =’ or ‘mass =’. Although most students convert the volume of a solution to dm3 for a titration calculation, far fewer did in this calculation, so their calculated number of moles was 1000 times the correct value.

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  Hydrogen chloride is fully ionised; about 1% of ethanoic acid ionises. A titration uses 0.0480 mol/dm3 ethanedioic acid and 25.0 cm3 sodium hydroxide. Equation: H₂C₂O₄+2NaOH -> Na₂C₂O₄+2H₂O.

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• AQA 8462 · November 2021 · Paper 2F · Q2 · 13 marks

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  A student evaporates 50 cm3 filtered seawater. Empty dish mass=30.44 g; dish plus dry salt=30.49 g. Student Y distils without a water-cooled condenser; student Z uses one.

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• AQA 8462 · November 2020 · Paper 1H · Q4 · 8 marks

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  [04.2] Only a third of students recognised that water provided the hydroxide ions. Vague references to the electrolyte were not sufficient.

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  Copper chromate solution contains blue Cu²⁺ ions and yellow CrO₄^2- ions. During electrolysis, solution by the positive electrode turns yellow and bubbles form; by the negative electrode it turns blue and a solid forms.

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• AQA 8462 · June 2019 · Paper 1F · Q4 · 10 marks

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  [04.5] Over 90% of students identified an electric toy as the most suitable use for a non- rechargeable cell.

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  A cell uses copper as one electrode and electrode X as cobalt, magnesium or zinc. Voltages are cobalt 0.62 V, magnesium 2.71 V, zinc 1.10 V.

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• AQA 8462 · June 2019 · Paper 1F · Q6 · 11 marks

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  [06.3] Approximately 70% of students calculated the relative formula mass correctly.

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  Tungsten forms by WO3+3H2->W+3H2O. Mr WO3=232, H2=2 and Ar W=184. Aluminium extraction data are also given.

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• AQA 8462 · June 2019 · Paper 1F · Q9 · 9 marks

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  [09.1] Approximately 50% of students correctly identified H+ as the ion produced by all acids in aqueous solution. The most common incorrect response was OH–

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  This question concerns acids, calcium hydroxide neutralisation and using titrations to compare sulfuric acid samples P and Q.

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• AQA 8462 · June 2019 · Paper 1H · Q2 · 9 marks

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  [02.4] Approximately 70% of students were able to take a correct reading from the burette scale. The most common incorrect answer was 28.4 cm3.

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  This question concerns acids, calcium hydroxide neutralisation and using titrations to compare sulfuric acid samples P and Q.

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• AQA 8462 · June 2019 · Paper 1H · Q6 · 9 marks

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  [06.2] Most students scored the 2 marks for the order of reactivity of the top four metals and the justification for this order. The most common error was then to put silver above copper in the order of reactivity. However, only a small proportion of students were able to explain the negative voltage for silver in terms of its reactivity compared with copper.

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  A cell uses copper as one electrode. Electrode X voltages: cobalt +0.62 V, copper 0.00, magnesium +2.71, nickel +0.59, silver -0.46, tin +0.48.

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• AQA 8462 · June 2019 · Paper 1H · Q9 · 8 marks

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  [09.1] Almost a half of students scored 0 marks. The mark scheme required the use of comparatives. Common correct responses were: • Better insulator • Less heat loss Common responses seen that were not credited included: • good insulator • no heat loss.

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  Sulfuric acid is added to 25.0 cm3 KOH in a polystyrene cup. A later run uses 15.5 cm3 of 0.500 mol/dm3 H2SO4. Equation: 2KOH+H2SO4->K2SO4+2H2O.

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• AQA 8462 · June 2018 · Paper 1F · Q4 · 5 marks

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  [04.4] All four statements about graphite were true and 70% of students could pick out ‘delocalised electrons’ as the reason for graphite’s electrical conductivity.

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  This question is about electrolysis and graphite electrodes.

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• AQA 8462 · June 2018 · Paper 1F · Q9 · 11 marks

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  [09.3] Whilst 56% of students achieved at least one mark, 34% of these students achieved both. • Many students repeated information in the stem of the question. And some appeared to ignore it as they declared sodium to be a non-metal. • Many gave differences in the structure of the atoms instead of differences in properties of the substances. • Some effectively gave the same difference twice, for example writing that sodium is soft on one line and iron is hard on the other.

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  A particle diagram of iron pyrites shows an iron:sulfur atom ratio of 1:2; iron-56 has atomic number 26. Nickel is extracted by carbon; atom-economy reactants have total Mr 87 and useful product Mr 59.

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• AQA 8462 · June 2018 · Paper 1H · Q1 · 8 marks

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  [01.3] This question discriminated well, with marks across the range being spread fairly equally. Whilst there were many excellent answers, a lot of students concentrated on the crystallisation phase, without saying how the magnesium sulfate solution would be produced. Some started by adding magnesium sulfate to an acid. A few students mixed unspecified quantities of magnesium oxide and sulfuric acid in an evaporating basin and then evaporated to dryness, sometimes stating that the acid was being evaporated off. Even when an oxide is correctly added in excess and the excess filtered off, evaporation to dryness will not yield crystals.

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  This question is about making soluble salts including calcium nitrate and magnesium sulfate crystals.

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• AQA 8462 · June 2018 · Paper 1H · Q2 · 11 marks

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  [02.1] Because the question asked for the formula rather than the empirical formula, an answer of Fe9S18 was accepted. Even so, 51% of students could not count the atoms and produce a ratio of 1:2. A formula was required, not an equation which some students provided.

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  A particle diagram of iron pyrites shows an iron:sulfur atom ratio of 1:2; iron-56 has atomic number 26. Nickel is extracted by carbon; atom-economy reactants have total Mr 87 and useful product Mr 59.

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• AQA 8462 · June 2018 · Paper 1H · Q3 · 5 marks

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  [03.2] 62% of students answered this question on a new area of the specification correctly. Many, however, mixed up the answers to questions 03.2 and 03.3. Many thought that charge, energy, or a product run out.

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  A simple cell uses copper and zinc in sodium chloride solution. This question compares alkaline batteries, hydrogen fuel cells and lithium-ion vehicle batteries.

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• AQA 8462 · June 2018 · Paper 1H · Q6 · 14 marks

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  [06.3] 58% of students did not achieve a mark for this question. The investigation was stated to be about the relationship between volume and time, but the diagram showed no means of measuring volume. The expected answer was to use inverted measuring cylinders so that volume (not ‘amount’) could be measured. Although it would pose practical difficulties, the idea of using gas syringes was also accepted (on the grounds that it could be made to work if they were attached to funnels placed over the electrodes). Many suggested changing the electrodes as graphite is not inert, suggesting a lack of understanding of the required practical. Some students suggested that the apparatus is upside down.

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  A student electrolyses zinc chloride using graphite. Hydrogen collection is steady at 0.45 cm3/min; chlorine initially collects more slowly, then at the same rate after about 8 min. At 20 min chlorine volume is 6.6 cm3. Gas molar volume=24 dm3.

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• AQA 8462 · June 2018 · Paper 1H · Q8 · 15 marks

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  [08.7] This difficult unstructured calculation tested a new area of the specification, and discriminated very well. 74% of students were able to achieve at least one mark, usually for calculating the Mr of TiCl4. 7% of students achieved all four marks, with 12% achieving at least three marks and there were some valiant efforts. Common errors were: • using 92 instead of 23 to calculate the number of moles of Na • omitting the unit conversion from kg to g for the mole calculations • using the 1:4 mole ratio incorrectly or not at all. Also, it is not appropriate to leave answers in the form of a fraction, even if this is the default on their calculator. Answers should always be converted to decimal form.

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  Titanium manufacture uses chlorine, titanium chloride, sodium and argon. Stage 2 reacts TiCl4 with 4Na. Ar Ti=48,Cl=35.5,Na=23; actual yield comparison uses theoretical 13.5 kg and 92.3%.

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• AQA 8462 · sample1 · Paper 1F · Q2 · 8 marks

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  A student compares zinc, copper and magnesium reactions with copper sulfate. Iron extraction uses the equation Fe2O3+C -> Fe+CO2.

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• AQA 8462 · sample1 · Paper 1F · Q3 · 4 marks

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  Lithium carbonate decomposes on heating and carbon dioxide is collected over water.

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• AQA 8462 · sample1 · Paper 1F · Q6 · 13 marks

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  Copper carbonate reacts with sulfuric acid to form copper sulfate, carbon dioxide and water. Useful-product Mr=159.5 and total reactant Mr=221.5.

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• AQA 8462 · sample1 · Paper 1H · Q7 · 11 marks

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  Sodium carbonate reacts with acid and CO2 volume plateaus at 95.0 cm3. Gas molar volume is 24000 cm3/mol.

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• AQA 8462 · sample1 · Paper 2H · Q9 · 6 marks

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  Marble chips react with hydrochloric acid. As the reaction proceeds, reactant concentration falls and surface area can decrease.

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