DP Chemistry (last assessment 2024)

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Question 19M.2.sl.TZ1.2b(i)

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

Benzoic acid, C6H5COOH, is another derivative of benzene.

(b(i))

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 «moldm−3»  [✔]

 

Note: Award [2] for correct final answer.

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Examiners report

Many students could correctly calculate the hydroxide concentration, but some weaker students calculated hydrogen ion concentration only.

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