Question 19M.3.hl.TZ2.1b(i)
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.3.hl.TZ2.1b(i) |
| Level | hl | 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+] in the solution has increased «over time»
OR
acid concentration has decreased «as reacted with lead»
OR
surface lead has decreased/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 a response that only discusses mathematical or proportional relationships.
A surprising number of candidates gave evidence for the non-linearity but then did not go on to explain why, giving no reasons or causes rooted in chemical theory. The command term "suggest" involves proposing a solution or hypothesis. Here the instruction "suggest why" indicates that the reason has to be explained.
