Question 19M.3.hl.TZ2.8
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.3.hl.TZ2.8 |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Determine, Outline, State | Question number | 8 | Adapted from | N/A |
Heavy metals are toxic even in very low concentrations.
Outline why heavy metals are toxic.
[1]
Any one of:
disrupt endocrine system
OR
compete for active sites of enzymes/cellular receptors
OR
form complexes with/inhibit enzymes
OR
denature proteins
OR
change shape of active site [✔]
participate in redox reactions
OR
disturb normal redox balance «in cells» [✔]
initiate «free» radical reactions «in electron transfer» [✔]
The candidates seemed to have difficulty in outlining why heavy metals are toxic.
Determine the maximum concentration of lead(II) ions at 298 K in a solution in which the concentration of carbonate ions is maintained at 1.10 × 10−4 mol dm−3. Use section 32 of the data booklet.
[2]
«Ksp = 7.40 × 10–14»
Ksp = [Pb2+][CO32–] [✔]
[Pb2+] «= » = 6.73 × 10–10 «mol dm–3» [✔]
Note: Award [2] for correct final answer.
Majority of the candidates managed to get two marks in determining the maximum concentration of lead(II) ions using solubility product constant.
State a method, other than precipitation, of removing heavy metal ions from solution.
[1]
Any one of:
chelation «by EDTA/polydentate ligand anchored» [✔]
ion exchange systems [✔]
adsorption by «water» plants [✔]
Note: Accept “use of zeolites”.
This was not well answered by most of the candidates.