DP Chemistry (last assessment 2024)

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Question 18M.2.sl.TZ1.5

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Date May 2018 Marks available [Maximum mark: 3] Reference code 18M.2.sl.TZ1.5
Level sl Paper 2 Time zone TZ1
Command term Justify, Predict, State Question number 5 Adapted from N/A
5.
[Maximum mark: 3]
18M.2.sl.TZ1.5

Limescale, CaCO3(s), can be removed from water kettles by using vinegar, a dilute solution of ethanoic acid, CH3COOH(aq).

(a)

Predict, giving a reason, a difference between the reactions of the same concentrations of hydrochloric acid and ethanoic acid with samples of calcium carbonate.

[2]

Markscheme

slower rate with ethanoic acid

OR

smaller temperature rise with ethanoic acid

 

[H+] lower

OR

ethanoic acid is partially dissociated

OR

ethanoic acid is weak

 

Accept experimental observations such as “slower bubbling” or “feels less warm”.

[2 marks]

(b)

Dissolved carbon dioxide causes unpolluted rain to have a pH of approximately 5, but other dissolved gases can result in a much lower pH. State one environmental effect of acid rain.

[1]

Markscheme

Any one of:

corrosion of materials/metals/carbonate materials

destruction of plant/aquatic life

«indirect» effect on human health

 

Accept “lowering pH of oceans/lakes/waterways”.

[1 mark]

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