DP Chemistry (last assessment 2024)

Question 17N.3.sl.TZ0.3c

Date	November 2017	Marks available	[Maximum mark: 2]	Reference code	17N.3.sl.TZ0.3c
Level	sl	Paper	3	Time zone	TZ0
Command term	Calculate	Question number	c	Adapted from	N/A

[Maximum mark: 2]

17N.3.sl.TZ0.3c

Sodium chloride, NaCl, can be spread on icy roads to lower the freezing point of water.

The diagram shows the effects of temperature and percentage by mass of NaCl on the composition of a mixture of NaCl and H₂O.

(c)

Calculate the percentage of water by mass in the NaCl•2H₂O crystals. Use the data from section 6 of the data booklet and give your answer to two decimal places.

[2]

Markscheme

M_r = 94.48

« $2\frac{{\left( {1.01 \times 2 + 16.00} \right)}}{{94.48}} \times 100 =$ » 38.15 «%»

Award M2 only if answer is to 2 decimal places.

Award [2] for correct final answer.

Award [1 max] for 38.10 %.

Syllabus sections

Core

Core » Topic 11: Measurement and data processing » 11.1 Uncertainties and errors in measurement and results

Core » Topic 1: Stoichiometric relationships » 1.2 The mole concept

Core » Topic 1: Stoichiometric relationships

Core » Topic 11: Measurement and data processing

Question 17N.3.sl.TZ0.3c

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