DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ1.d(i)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ1.d(i)
Level hl Paper 2 Time zone TZ1
Command term Sketch Question number d(i) Adapted from N/A
d(i).
[Maximum mark: 2]
19M.2.hl.TZ1.d(i)

Both vinegar (a dilute aqueous solution of ethanoic acid) and bleach are used as cleaning agents.

Sketch a graph of pH against volume of hydrochloric acid added to ammonia solution, showing how you would determine the pKa of the ammonium ion.

 

[2]

Markscheme

correct shape of graph AND vertical drop at Vn    [✔]

pKa = pH at Vn 2 /half neutralization/half equivalence    [✔]

 

Note: M1: must show buffer region at pH > 7 and equivalence point at pH < 7. Graph must start below pH = 14.

Examiners report

Quite poorly done with many candidates not indicating a vertical drop but rather a weak acid/weak base curve. Some did not have the correct location for the equivalence point.

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