O-LevelChemistryOrganic Chemistry5070/22 · Oct/Nov 2018 · Q37 Marks
The structure of fumaric acid is shown. [Figure 3.1: A molecule showing two carboxylic acid groups connected by a carbon-carbon double bond: HO-C(=O)-CH=CH-C(=O)-O-H (trans isomer).]
- (a)How does this structure show that fumaric acid is an unsaturated compound?[1]
- (b)Fumaric acid is oxidised by acidified aqueous potassium manganate(VII). What colour change would you observe in the reaction mixture when excess aqueous fumaric acid is added to acidified aqueous potassium manganate(VII)? from .......... to ..........[2]
- (c)Fumaric acid is neutralised by aqueous sodium hydroxide. C₂H₂(COOH)₂ + 2NaOH → C₂H₂(COONa)₂ + 2H₂O
- (c)(i)Write the ionic equation for this reaction.[1]
- (c)(ii)Calculate the volume of 0.0500 mol/dm³ sodium hydroxide required to neutralise 20.0 cm³ of 0.0200 mol/dm³ fumaric acid. Give your answer to three significant figures. volume .......... cm³[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [1] (a) has a carbon-carbon double bond / has a C=C bond
- [1] (b) purple (1)
- [1] (b) (to) colourless (1)
- [1] (c)(i) H⁺ + OH⁻ → H₂O
- [1] (c)(ii) moles fumaric acid = 4.00 × 10⁻⁴ (1)
- [1] (c)(ii) moles sodium hydroxide = 8.00 × 10⁻⁴ (1)
- [1] (c)(ii) 16.0 (cm³) (1)
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