DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ1.2e

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ1.2e
Level hl Paper 2 Time zone TZ1
Command term Outline, Suggest Question number e Adapted from N/A
e.
[Maximum mark: 2]
19M.2.hl.TZ1.2e

Benzoic acid, C6H5COOH, is another derivative of benzene.

(e)

Outline why both C to O bonds in the conjugate base are the same length and suggest a value for them. Use section 10 of the data booklet.

[2]

Markscheme

electrons delocalized «across the O–C–O system»

OR

resonance occurs [✔]

122 «pm» < C–O < 143 «pm» [✔]

 

Note: Accept “delocalized π-bond”.
Accept “bond intermediate between single and double bond” or “bond order 1.5” for M1.
Accept any answer in range 123 to 142 pm.

Examiners report

This question was a challenge. Candidates were not able to explain the intermediate bond length and the majority suggested the value of either the bond length of C to O single bond or double bond.

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