Calculations involving gas volumes
4 marks · NormalCalcium carbonate reacts with hydrochloric acid as shown in the equation:
State the volume of carbon dioxide gas produced (in cm³ at rtp) from 0.10 mol of calcium carbonate.
Give one reason why the actual volume of gas collected might be less than the calculated value.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 2,400 cm³
(b) Some gas escapes, or the reaction was incomplete, or not all acid reacted, or temperature and pressure were not exactly at rtp · must show Any valid reason
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Marking points
M1 (a) · 1 mark · Uses correct molar volume at rtp (24,000 cm³ per mole, or 24 dm³ per mole and conversion)
A1 (a) · 1 mark · Correct answer: 2,400 cm³, with unit (accept 2400)
B1 (b) · 1 mark · Gives any correct reason why the measured volume may be less (e.g. some gas escapes)
B2 (b) · 1 mark · Gives a second valid, different point or elaborates (e.g. reaction not complete, not all acid reacted, rtp conditions not met)
Worked solution
a) 1 mole of CaCO₃ gives 1 mole CO₂. So 0.10 mol gives 0.10 mol CO₂.
At rtp, 1 mol gas = 24,000 cm³.
b) Some gas may escape before it is fully collected. The reaction may not be complete. Temperature may not be exactly at rtp.