A-LevelChemistryPolymerisation9701/42 · Feb/Mar 2018 · Q717 Marks

Complete the equations to show the two types of polymerisation. Draw one repeat unit for each polymer. Include any other products. • addition polymerisation nCH2=CHCH3(g) → [Box for polymer] • condensation polymerisation nHO2CCH2CO2H(s) + nHOCH2CH2OH(I) → [Box for polymer]

(a)(i)Complete the equations to show the two types of polymerisation. Draw one repeat unit for each polymer. Include any other products. • addition polymerisation nCH2=CHCH3(g) → [Box for polymer] • condensation polymerisation nHO2CCH2CO2H(s) + nHOCH2CH2OH(I) → [Box for polymer][3]
(a)(ii)Suggest the sign of the entropy changes, ΔSº, for each of the two types of polymerisation. Explain your answers. • ΔSº for addition polymerisation • ΔSº for condensation polymerisation[2]
(b)(i)An amide bond forms when a carboxylic acid reacts with an amine. Complete the equation by writing the products in the box. R-CO₂H + H₂N-R' → [Box for products][1]
(b)(ii)Use your answer to (i) to work out the bonds that are broken and the bonds that are formed during the reaction between a carboxylic acid and an amine. • bonds that are broken • bonds that are formed[2]
(b)(iii)Use bond energy values from the Data Booklet to calculate the enthalpy change, ΔH°, when one mole of amide bonds is formed in the reaction in (i). ΔH° = ______ kJ[2]
(c)Amide bonds can also be formed by reacting acyl chlorides with amines. The enthalpy change for this process, ΔH°, is −6.00 kJ mol⁻¹. Calculate the minimum entropy change, ΔS, for this reaction to be spontaneous (feasible) at 298 K. ΔS = ______ J K⁻¹ mol⁻¹[2]
(d)(i)The repeat unit of the polyamide Kevlar is shown. [Figure of Kevlar repeat unit] The monomers of Kevlar, benzene-1,4-dioic acid and 1,4-diaminobenzene, can be synthesised as follows. [Figure showing synthesis of benzene-1,4-dioic acid from H3C-benzene-CH3 via reaction 1, and 1,4-diaminobenzene from O2N-benzene-NO2 via reaction 2] State the reagents and conditions needed for: reaction 1[1]
(d)(ii)reaction 2[2]
(e)Kevlar is both strong and rigid. Complete the table to identify two intermolecular forces and the groups involved which are responsible for these properties of Kevlar. [Table with columns 'intermolecular force' and 'group(s) involved'][2]

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 2018). The mark or mark type is shown in brackets.

[3] [Addition polymer: one repeat unit showing -CH(CH₃)-CH₂-. Condensation polymer: one repeat unit showing -O-CH₂CH₂-O-CO-CH₂-CO-, plus nH₂O as a product.]
[2] • for addition polymerisation: ΔS will be negative, as many gas molecules are combining to form one (large) molecule • for condensation polymerisation: ΔS likely to be positive, (as each pair of monomer molecules join to chain, two molecules of) water forms
[1] (RCO2H + H2NR' — →) RCONHR' + H2O
[2] broken: C-O, N-H formed: C-N, O-H
[2] bonds formed: 305 + 460 or 765 bonds broken: 360 + 390 or 750 (both) ΔH = 750 – 765 = −15 (kJ)
[2] (If ∆G = 0, then) ∆H = T∆S ∆S = ∆H/T = −6000/298 = −20.1 (J mol⁻¹ K⁻¹)
[1] heat with (conc.) KMnO4
[2] Sn and HCl heat + conc. (then add NaOH)
[2] intermolecular force | group(s) involved --------------------|-------------------- hydrogen bonding | N-H and C=O (of amide) induced dipole / van der Waals | benzene rings