Question 18M.3.sl.TZ1.2b
| Date | May 2018 | Marks available | [Maximum mark: 1] | Reference code | 18M.3.sl.TZ1.2b |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Outline | Question number | b | Adapted from | N/A |
Students were asked to investigate how a change in concentration of hydrochloric acid, HCl, affects the initial rate of its reaction with marble chips, CaCO3.
They decided to measure how long the reaction took to complete when similar chips were added to 50.0 cm3 of 1.00 mol dm−3 acid and 50.0 cm3 of 2.00 mol dm−3 acid.
Two methods were proposed:
(1) using small chips, keeping the acid in excess, and recording the time taken for the solid to disappear
(2) using large chips, keeping the marble in excess, and recording the time taken for bubbles to stop forming.
Neither method actually gives the initial rate. Outline a method that would allow the initial rate to be determined.
[1]
measure the volume of gas at different times «plot a graph and extrapolate»
OR
measure the mass of the reaction mixture at different times «plot a graph and extrapolate»
Accept other techniques that yield data which can be plotted and extrapolated.
[1 mark]
