DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ2.b

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Date May 2019 Marks available [Maximum mark: 1] Reference code 19M.2.hl.TZ2.b
Level hl Paper 2 Time zone TZ2
Command term State Question number b Adapted from N/A
b.
[Maximum mark: 1]
19M.2.hl.TZ2.b

Carbonated water is produced when carbon dioxide is dissolved in water under pressure. The following equilibria are established.

Equilibrium (1)  CO2 (g)  CO2 (aq)

Equilibrium (2)  CO2 (aq) + H2O (l) H+ (aq) + HCO3− (aq)

When a bottle of carbonated water is opened, these equilibria are disturbed.

State, giving a reason, how a decrease in pressure affects the position of Equilibrium (1).

[1]

Markscheme

shifts to left/reactants AND to increase amount/number of moles/molecules of gas/CO2 (g)    [✔]

 

Note: Accept “shifts to left/reactants AND to increase pressure”.

Examiners report

Many students gave generic responses referring to a correct shift without conveying the idea of compensation or restoration of pressure or moles of gas. This generic reply reflects the difficulty in applying a theoretical concept to the practical situation described in the question.

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