Question 22N.2.sl.TZ0.c
| Date | November 2022 | Marks available | [Maximum mark: 2] | Reference code | 22N.2.sl.TZ0.c |
| Level | sl | Paper | 2 | Time zone | TZ0 |
| Command term | Suggest | Question number | c | Adapted from | N/A |
Lignite, a type of coal, contains about 0.40 % sulfur by mass.
Sodium thiosulfate reacts with hydrochloric acid as shown:
Na2S2O3 (aq) + 2HCl (aq) → S (s) + SO2 (aq) + 2NaCl (aq) + H2O (l)
The precipitate of sulfur makes the mixture cloudy, so a mark underneath the reaction mixture becomes invisible with time.
Suggest two variables, other than concentration, that should be controlled when comparing relative rates at different temperatures.
[2]
Any two of:
depth/volume «of solution» ✔
colour/darkness/thickness/size/background of mark ✔
intensity of lighting in the lab ✔
Accept same size flask.
Accept position of observation/person observing.
Accept same equipment/apparatus.
Do not accept catalyst/particle size/pressure/time.
Most candidates mentioned "volume" as a variable that should be controlled gaining one of the two marks, while only a small proportion of candidates seemed to understand how the experiment worked and discussed the lighting in the room and the thickness of the mark. The most common incorrect answer was "pressure" which was irrelevant to this experiment.
