DP Chemistry (last assessment 2024)

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Question 19M.1.hl.TZ2.27

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Date May 2019 Marks available [Maximum mark: 1] Reference code 19M.1.hl.TZ2.27
Level hl Paper 1 Time zone TZ2
Command term Question number 27 Adapted from N/A
27.
[Maximum mark: 1]
19M.1.hl.TZ2.27

The following equation represents the dissociation of water at 25 °C.

2H2O (l) ⇌ H3O+ (aq) + OH− (aq)        ΔH = +56 kJ

Which changes occur as the temperature increases?

A. [H3O+] increases and pH will decrease.

B. [H3O+] decreases and pH will increase.

C. [H3O+] increases and pH will increase.

D. [H3O+] decreases and pH will decrease.

[1]

Markscheme

A

Examiners report

This is one of the more challenging questions on the paper. 62 % of the candidates obtained the correct answer. The most commonly chosen distractor was C, where the increase in the concentration of H3O+ was recognized by applying Le Chatelier’s principle but the effect on pH was incorrect.

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