DP Chemistry (last assessment 2024)

Question 22M.2.sl.TZ1.2e(ii)

Date	May 2022	Marks available	[Maximum mark: 2]	Reference code	22M.2.sl.TZ1.2e(ii)
Level	sl	Paper	2	Time zone	TZ1
Command term	Determine	Question number	e(ii)	Adapted from	N/A

e(ii).

[Maximum mark: 2]

22M.2.sl.TZ1.2e(ii)

Ammonia, NH₃, is industrially important for the manufacture of fertilizers, explosives and plastics.

Ammonia is soluble in water and forms an alkaline solution:

NH₃(g) + H₂O (l) $⇌$ NH₄⁺(aq) + HO^–(aq)

(e(ii))

Determine the concentration, in mol dm^–3, of the solution formed when 900.0 dm³ of NH₃(g) at 300.0 K and 100.0 kPa, is dissolved in water to form 2.00 dm³ of solution. Use sections 1 and 2 of the data booklet.

[2]

Markscheme

amount of ammonia $⟨ ⟨ = \frac{P . V}{R . T} = \frac{100.0 k P a \times 900.0 d m^{3}}{8.31 J K^{- 1} m o l^{- 1} \times 300.0 K} ⟩ ⟩ = 36.1 « mol »$ ✔

concentration $⟨ ⟨ = \frac{n}{V} = \frac{36.1}{2.00} ⟩ ⟩ = 18.1 « mol {dm}^{- 3} »$ ✔

Award [2] for correct final answer.

Examiners report

About 40% of candidates gained full marks for the calculation and a significant number of others gained the second mark to calculate the concentration as an ECF.

Syllabus sections

Core

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

Core » Topic 1: Stoichiometric relationships

Question 22M.2.sl.TZ1.2e(ii)

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