O-LevelChemistryOrganic Chemistry5070/21 · Oct/Nov 2021 · Q810 Marks

The structure of angelic acid is shown. H₃C C-OH C C H CH₃ [Figure 8.1]

(a)Explain how this structure shows that angelic acid is an unsaturated compound.[1]
(b)Deduce the molecular formula of angelic acid.[1]
(c)(i)Angelic acid is a weak acid. Define the term acid.[1]
(c)(ii)Explain the meaning of the term weak as applied to acids.[1]
(d)(i)Angelic acid can be polymerised. State the name of the type of polymerisation that occurs.[1]
(d)(ii)Draw the partial structure of the polymer of angelic acid. Show two repeat units.[2]
(e)Angelic acid reacts with methanol, CH₃OH, to form an ester. Complete the structure of this ester to show all the atoms and all the bonds. [Figure 8.2][1]
(f)Construct the equation for the complete combustion of methanol.[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] 8(a) has C=C bond / has a carbon-carbon double bond
[1] 8(b) C5H8O2
[1] 8(c)(i) (solution which) contains hydrogen ions / hydrogen ion donor
[1] 8(c)(ii) (acid which) is incompletely ionised / (acid which) is not completely dissociated
[1] 8(d)(i) addition
[2] 8(d)(ii) (diagram for polymer, showing two repeat units of (-CH(CH₃)-C(CH₃)(COOH)-))
[1] 8(e) (diagram completed with C(=O)OCH₃ group)
[1] 8(f) correct formulae (2CH₃OH + 3O₂ → 2CO₂ + 4H₂O)
[1] 8(f) balancing

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