DP Chemistry (last assessment 2024)

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

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

Benzoic acid, C6H5COOH, is another derivative of benzene.

The pH of an aqueous solution of benzoic acid at 298 K is 2.95. Determine the concentration of hydroxide ions in the solution, using section 2 of the data booklet.

[2]

Markscheme

ALTERNATIVE 1:
[H+] «= 10−2.95» = 1.122 × 10−3 «mol dm−3» [✔]


«[OH−] =  1.00 × 10 − 14  mo l 2  d m − 6 1.22 × 10 − 3  mol d m − 3 =» 8.91 × 10−12 «mol dm−3» [✔]

 

ALTERNATIVE 2:
pOH = «14 − 2.95 =» 11.05 [✔]
«[OH−] = 10−11.05 =» 8.91 × 10−12 «mol dm−3» [✔]

 

Note: Award [2] for correct final answer.
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Examiners report

Generally well done with a few calculating the pOH rather than the concentration of hydroxide ion asked for.

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