A-LevelChemistryPolymerisation9701/42 · Feb/Mar 2021 · Q610 Marks

Fumaric acid is a naturally occurring dicarboxylic acid. [Figure 6.1]

(a)Identify the products of the reaction between fumaric acid and an excess of hot, concentrated, acidified manganate(VII).[1]
(b)(i)Fumaric acid can form addition and condensation polymers. Draw the repeat unit of the addition polymer poly(fumaric acid).[1]
(b)(ii)Draw the repeat unit of the polyester formed when fumaric acid reacts with ethane-1,2-diol, (CH₂OH)₂. The ester bond should be shown fully displayed.[2]
(b)(iii)Explain why polyesters normally biodegrade more readily than polyalkenes.[1]
(c)Fumaric acid reacts with cold, dilute, acidified manganate(VII) to form compound P. [Figure 6.2] Only three stereoisomers of P exist. One of the stereoisomers is shown. [Figure 6.3] Complete the three-dimensional diagrams in the boxes to show the other two stereoisomers of P. [Figure 6.4][2]
(d)The enzyme fumarase catalyses the reaction of fumarate ions, C₄H₂O₄²⁻, with water to form malate ions, C₄H₄O₅²⁻. C₄H₂O₄²⁻ + H₂O ⇌ C₄H₄O₅²⁻ Describe, with the aid of a suitably labelled diagram, how an enzyme such as fumarase can catalyse a reaction.[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 (Feb/Mar 2021). The mark or mark type is shown in brackets.

[1] Carbon dioxide (CO₂) and water (H₂O)
[1] Correct repeat unit showing the double bond of fumaric acid opening up to form a saturated chain with -COOH groups branching off.
[2] M1: Correct ester linkage (-COO- or -OCO-) shown fully displayed.
[2] M2: Rest of the repeat unit correct, derived from fumaric acid and ethane-1,2-diol.
[1] Polyesters contain polar ester linkages (or hydrolysable bonds) that can be broken down by hydrolysis, whereas polyalkenes have non-polar C-C bonds that are resistant to hydrolysis / biodegrade via different mechanisms (e.g. oxidation).
[2] Correct three-dimensional drawings of the enantiomer of the given structure and the meso-compound, showing correct relative stereochemistry for the two chiral centres.
[3] M1: Diagram showing an enzyme with an active site, and a substrate with a complementary shape. (Labelled active site, substrate, enzyme).
[3] M2: Substrate binds/bonds/fits into the active site of the enzyme (forming enzyme-substrate complex).
[3] M3: Reaction occurs, products are formed and released from the active site, and the enzyme is regenerated (unchanged).

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.