DP Chemistry (last assessment 2024)

Question 21M.2.sl.TZ1.2c

Date	May 2021	Marks available	[Maximum mark: 3]	Reference code	21M.2.sl.TZ1.2c
Level	sl	Paper	2	Time zone	TZ1
Command term	Determine, State	Question number	c	Adapted from	N/A

[Maximum mark: 3]

21M.2.sl.TZ1.2c

Iron (II) sulfide reacts with hydrochloric acid to form hydrogen sulfide, H₂S.

(c)

A gaseous sample of nitrogen, contaminated only with hydrogen sulfide, was reacted with excess sodium hydroxide solution at constant temperature. The volume of the gas changed from 550 cm³ to 525 cm³.

Determine the mole percentage of hydrogen sulfide in the sample, stating one assumption you made.

[3]

Markscheme

Mole percentage H₂S:
volume of H₂S = «550 − 525 = » 25 «cm³» ✔
mol % H₂S = « $\frac{25 {cm}^{3}}{550 {cm}^{3}} \times 100$ = » 4.5 «%» ✔

Award [2] for correct final answer of 4.5 «%»

Assumption:
«both» gases behave as ideal gases ✔

Accept “volume of gas $α$ mol of gas”.
Accept “reaction goes to completion”.
Accept “nitrogen is insoluble/does not react with NaOH/only H₂S reacts with NaOH”.

Syllabus sections

Core

Core » Topic 1: Stoichiometric relationships » 1.3 Reacting masses and volumes

Core » Topic 1: Stoichiometric relationships

Question 21M.2.sl.TZ1.2c

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