Date | November 2018 | Marks available | 1 | Reference code | 18N.3.sl.TZ0.3 |
Level | SL | Paper | 3 | Time zone | TZ0 |
Command term | State | Question number | 3 | Adapted from | N/A |
Question
The presence of very small amounts of lead in calcium-based antacids can be determined using inductively coupled plasma-mass spectroscopy (ICP-MS).
State the type of particle present in the plasma formed.
An unknown antacid sample has a lead ion concentration of 0.50 μg dm‒3.
Calculate the concentration of lead ions in the sample in mol dm‒3.
Electrolysis is used to obtain lead from Pb2+ (aq) solution.
Determine the time, in hours, required to produce 0.0500 mol lead using a current (I) of 1.34 A. Use section 2 of the data booklet and the equation, charge (Q) = current (I) × time (t, in seconds).
Markscheme
positive ions/cations/Pb2+
OR
free electrons ✔
Accept “ions” OR “charged species/particle”.
[Pb2+] = 0.50 × 10‒6/5.0 × 10–7 «g dm–3» ✔
[Pb2+] «» = 2.4 × 10‒9 «mol dm‒3» ✔
Award [2] for correct final answer.
«Faraday’s constant, F = 9.65 × 104 C mol‒1 and 1 A = 1 C s–1»
Q «= 0.0500 mol × 2 × 96500 C mol‒1» = 9650 «C» ✔
t « so » = 2.00 «hours» ✔
Award [2] for correct final answer.