DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ2.d(ii)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ2.d(ii)
Level hl Paper 2 Time zone TZ2
Command term Predict Question number d(ii) Adapted from N/A
d(ii).
[Maximum mark: 2]
19M.2.hl.TZ2.d(ii)

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)

Soda water has sodium hydrogencarbonate, NaHCO3, dissolved in the carbonated water.

Predict, referring to Equilibrium (2), how the added sodium hydrogencarbonate affects the pH.(Assume pressure and temperature remain constant.)

[2]

Markscheme

«additional HCO3-» shifts position of equilibrium to left   [✔]

pH increases   [✔]

 

Note: Do not award M2 without any justification in terms of equilibrium shift in M1.

Examiners report

A significant number of candidates omitted the “equilibrium” involved in the dissolution of a weak base.

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