Question 19M.3.sl.TZ2.1b(i)
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.3.sl.TZ2.1b(i) |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Suggest | Question number | b(i) | Adapted from | N/A |
This question is about a mug made of a lead alloy.
The rate of lead dissolving in common beverages with various pH values was analysed.
Suggest why the relationship between time and lead concentration for Cola at 16 °C is not linear.
[1]
equilibrium is being established «between lead in solution and in mug»
OR
solution becoming saturated
OR
concentration of lead ions/[Pb2+] has increased «over time»
OR
acid concentration has decreased «as reacted with lead»
OR
surface lead has decrease/formed a compound/forms insoluble layer on surface
OR
acid reacts with other metals «because it is an alloy» [✔]
Note: Do not accept “concentration of cola, orange juice, etc… has decreased”.
Do not accept responses that only discusses mathematical or proportional relationships.
Many candidates struggled with this question, answering it from a mathematical perspective rather than explaining why the rate would decrease over time from a chemical perspective. There were several possible correct answers (reaching equilibrium, acid concentration decreasing, solution becoming saturated with lead ions, etc.…)
