| Date | May 2017 | Marks available | 2 | Reference code | 17M.3.hl.TZ1.10 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Outline | Question number | 10 | Adapted from | N/A |
Question
Antimony and its compounds are toxic, so it is important to check that the catalyst is removed from the final product. One technique to detect antimony is Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).
Outline the nature of the plasma state and how it is produced in ICP-MS.
Hydrogen sulfide could be used to remove antimony(III) ions from a solution.
Determine the concentration of antimony(III) ions that would be required to precipitate antimony(III) sulfide in a solution saturated with hydrogen sulfide.
[S2−] in water saturated with hydrogen sulfide = 1.0 × 10−14 mol dm−3
Ksp (Sb2S3) = 1.6 × 10−93
Identify a ligand that could be used to chelate antimony(III) ions in solution.
Markscheme
electrons AND positive ions «in gaseous state»
high frequency/alternating current passed through argon
OR
«oscillating» electromagnetic/magnetic field
OR
high frequency radio waves
Accept “gas” instead of “argon”.
[2 marks]
Ksp = [Sb3+]2 \( \bullet \) [S2−]3
[Sb3+]2 \( \bullet \) (10−14)3 = 1.6 x 10−93
[Sb3+] «\( = \sqrt {1.6 \times {{10}^{ - 51}}} \)» = 4.0 x 10−26 «mol dm−3»
Award [3] for correct final answer.
[3 marks]
EDTA/ethylenediaminetetraacetic aci
OR
H2N–CH2–CH2–HN2/ethane-1,2-diamine
Accept “EDTA4–”.
Accept other chelating agents.
[1 mark]
