DP Chemistry (last assessment 2024)

Question 19N.2.hl.TZ0.b

Date	November 2019	Marks available	[Maximum mark: 3]	Reference code	19N.2.hl.TZ0.b
Level	hl	Paper	2	Time zone	TZ0
Command term	Determine, Solve	Question number	b	Adapted from	N/A

[Maximum mark: 3]

19N.2.hl.TZ0.b

Copper forms two chlorides, copper(I) chloride and copper(II) chloride.

Solid copper(II) chloride absorbs moisture from the atmosphere to form a hydrate of formula CuCl₂• $x$ H₂O.

A student heated a sample of hydrated copper(II) chloride, in order to determine the value of $x$ . The following results were obtained:

Mass of crucible = 16.221 g
Initial mass of crucible and hydrated copper(II) chloride = 18.360 g
Final mass of crucible and anhydrous copper(II) chloride = 17.917 g

Determine the value of $x$ .

[3]

Markscheme

mass of H₂O = «18.360 g – 17.917 g =» 0.443 «g» AND mass of CuCl₂ = «17.917 g – 16.221 g =» 1.696 «g» ✔

moles of H₂O = « $\frac{{0.443{\text{g}}}}{{18.02{\text{g mo}}{{\text{l}}^{ - 1}}}}$ =» 0.0246 «mol»
OR
moles of CuCl₂ =« $\frac{{1.696{\text{g}}}}{{134.45{\text{g mo}}{{\text{l}}^{ - 1}}}}$ = » 0.0126 «mol» ✔

«water : copper(II) chloride = 1.95 : 1»

« $x$ =» 2 ✔

NOTE: Accept « $x$ =» 1.95.

NOTE: Award [3] for correct final answer.

Syllabus sections

Core

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

Core » Topic 1: Stoichiometric relationships

Question 19N.2.hl.TZ0.b

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