Calculate the mass, in g, of anhydrous sodium carbonate (Mr = 106.0) needed to prepare 250 cm3 of 0.150 mol dm−3 sodium carbonate solution.
[1 mark]
Total for this question: 1
Chemistry
Amount of substance
AQA 3.1.2
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The topic on one screen
- One mole = 6.022 × 1023 particles (the Avogadro constant). Moles link every quantity in this topic: m = n × Mr.
- Solutions: n = c × V, with V in dm3 — the cm3 → dm3 conversion is the single most common dropped mark.
- Gases: pV = nRT with p in Pa, V in m3, T in K. Convert units before you substitute, not after.
- Empirical formula = simplest whole-number ratio. Divide each % by Ar, then divide through by the smallest.
- Titrations: moles of known → ratio from the balanced equation → moles of unknown → concentration.
- Percentage uncertainty = (uncertainty ÷ measured value) × 100, summed per piece of apparatus — not per total volume.
Where students actually lose marks
Mass-for-a-standard-solution calculations were answered well except for one thing: forgetting to convert 250 cm3 to 0.250 dm3 before using n = c × V.
June 2023 Paper 1 examiner report (Q06.1)
Describing how to make a standard solution loses marks in predictable places: making the solution up in the beaker instead of transferring to a volumetric flask, skipping the rinse-and-transfer of washings, and forgetting to invert the flask to mix.
June 2023 Paper 1 examiner report (Q06.2)
Only 30% of students got full marks on the titration calculation. The killers: using the wrong Mr, ignoring the 2:1 ratio in the equation, and dividing by the wrong volume at the final step.
June 2023 Paper 1 examiner report (Q06.5)
Percentage uncertainty answers were generally poor — most students added both uncertainties and divided by the combined volume. Each apparatus gets its own % first; then you add the percentages.
June 2023 Paper 1 examiner report (Q06.6)
Try it — exam-style
Easy
ORIGINAL · after June 2023 Paper 1 Q06.1
Medium
ORIGINAL · after June 2023 Paper 1 Q06.2
The solid is dissolved in a beaker containing about 100 cm3 of distilled water. Describe how this solution is used to make exactly 250 cm3 of standard solution.
[3 marks]
Total for this question: 3
Hard
ORIGINAL · after June 2023 Paper 1 Q06.5
0.663 g of anhydrous sodium carbonate (Mr = 106.0) is dissolved and made up to 250 cm3. A 25.0 cm3 portion reacts with exactly 23.30 cm3 of hydrochloric acid: Na2CO3 + 2HCl → 2NaCl + H2O + CO2. Calculate the concentration of the hydrochloric acid.
[3 marks]
Total for this question: 3
Medium
ORIGINAL · after June 2023 Paper 1 Q06.6
The uncertainty in a 25.0 cm3 pipette reading is ±0.05 cm3. The total uncertainty in a 21.40 cm3 burette titre is ±0.10 cm3. Calculate the total percentage error.
[1 mark]
Total for this question: 1
Medium
ORIGINAL · after June 2023 Paper 2 Q08.4
A compound contains 54.53% carbon and 9.15% hydrogen by mass. The rest is oxygen. Calculate its empirical formula.
[3 marks]
Total for this question: 3
Easy
ORIGINAL
Calculate the volume, in dm3, occupied by 0.0350 mol of an ideal gas at 100 kPa and 298 K. (R = 8.31 J K−1 mol−1)
[2 marks]
Total for this question: 2
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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