Experiments to measure the rate of reaction
3 marks · EasyThe table below shows part of an experiment where the mass of carbon dioxide lost was measured every minute as marble chips reacted with dilute hydrochloric acid.
| Time / min | Mass of CO2 lost / g |
|---|---|
| 0 | 0.00 |
| 1 | 0.38 |
| 2 | 0.59 |
| 3 | 0.68 |
| 4 | 0.71 |
Calculate the average rate of reaction between 1 and 2 minutes, giving your answer in g/min.
At which time interval was the reaction fastest? Give your reasoning.
Suggest one practical reason why the mass measured might not decrease exactly as expected.
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.
Show answer
(a) 0.21 g/min · must show calculation of (0.59-0.38)/1
(b) Between 0 and 1 minute; reaction fastest at start because rate is greatest when reactants are most concentrated. · must show 0–1 min, between 0 and 1 minute, fastest at start
(c) Loss of liquid through spitting; not all carbon dioxide escapes instantly; cotton wool blocks some gas; measurement error; acid splashed out.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct calculation: (0.59-0.38)/1 = 0.21 g/min.
B1 (b) · 1 mark · States first interval (0-1 minute). Reason: reaction fastest at start.
B1 (c) · 1 mark · States a sensible practical reason for mass not decreasing exactly as theory predicts (e.g. splashing acid, slow gas loss, cotton wool reduces escape).
Worked solution
b) The reaction was fastest during the first minute (0–1 min) because the reactants are most concentrated at the start. c) Mass might not decrease as expected if some acid splashes out, or if gas escapes more slowly through the cotton wool.