A-LevelChemistryCarboxylic acids and derivatives9701/42 · May/June 2022 · Q811 Marks

Compare the relative acidities of ethanol, ethanoic acid, chloroethanoic acid and phenol. Explain your reasoning.

(a)Compare the relative acidities of ethanol, ethanoic acid, chloroethanoic acid and phenol. Explain your reasoning.[4]
(b)An excess of ethanedioic acid, HOOCCOOH(aq), is reacted with warm acidified KMnO4(aq). State the type of reaction undergone by ethanedioic acid. Describe what you would observe. Write an equation for this reaction. Your equation can use [O] or [H] as necessary.[2]
(c)A section of a polyester is shown. [Figure polyester, Fig. 8.1] Draw the structures of the two monomers that form this polyester.[2]
(d)Serine can polymerise to form two different types of condensation polymer; a polyester and a polypeptide. [Figure serine, Fig. 8.2] Draw the structure of the polypeptide showing two repeat units. The peptide linkage should be shown displayed.[2]
(e)Explain why condensation polymers normally biodegrade more readily than addition polymers.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[4] M1 chloroethanoic acid > ethanoic acid > phenol > ethanol
[4] M2 correct link of acidity once can be implied from M1 weakens O-H / carboxylate anion stabilised
[4] M3 / M4 explanation linked to structure (CICH2CO2H > ethanoic acid) due to electronegative / electron withdrawing / negative inductive effect of Cl
[4] M3 / M4 explanation linked to structure (ethanoic acid > phenol) due to electronegative / electron withdrawing / negative inductive effect of COOH / C=O
[4] M3 / M4 explanation linked to structure (phenol > ethanol) due to lone pair of oxygen overlapping / delocalised into the ring
[4] M3 / M4 explanation linked to structure (ethanol weakest) alkyl group is electron donating / positive inductive effect
[2] oxidation
[2] (solution) decolourises OR purple → colourless / pale pink OR bubbles
[2] HOOCCOOH + [O] → 2CO2 + H2O OR 5HOOCCOOH + 2MnO4 + 6H+ → 10CO2 + 8H2O + 2Mn2+
[2] M1 [Figure of HO-CH2-CH2-OH]
[2] M2 [Figure of HOOC-CH(CH3)-COOH]
[2] M1 peptide linkage shown displayed with saturated C each side
[2] M2 rest of structure correct AND continuation bonds
[1] addition polymers do not hydrolyse OR condensation polymers can hydrolyse

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