Question 22M.1.sl.TZ1.17
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.1.sl.TZ1.17 |
| Level | sl | Paper | 1 | Time zone | TZ1 |
| Command term | State | Question number | 17 | Adapted from | N/A |
A student was investigating rates of reaction. In which of the following cases would a colorimeter show a change in absorbance?
A. KBr (aq) + Cl2 (aq)
B. Cu (s) + Na2SO4 (aq)
C. HCl (aq) + NaOH (aq)
D. (CH3)3COH (aq) + K2Cr2O7 (aq)
[1]
A
Question 17 was the question about the colorimeter), which many teachers felt was unfair, and only 22% of students gave the correct answer. The complaints about the question were often based on the lack of familiarity with the colorimeter. However, Chemistry is a practical course and student should be exposed to a piece of equipment such as this. Also, it was felt that there was a lot to process in this question. Although answer C could fairly easily be eliminated as there is no colour change. Students then had to recognize that in D, alcohol oxidation would result in a colour change from orange to green, except that it is a tertiary alcohol. This left A and B. A is of course the right answer as chlorine replaces bromine, but if B actually happened, there would also be a colour change from clear to blue. So, students needed to remember that copper is below sodium on the activity series.