A-LevelChemistryCarbonyl compounds9701/22 · Feb/Mar 2023 · Q321 Marks

Alkenes undergo an addition reaction with a 1:1 mixture of CO and H₂ to form aldehydes. Fig. 3.1 shows the reaction of propene with a 1:1 mixture of CO and H2. [Fig. 3.1]

(a)(i)Define addition reaction.[1]
(a)(ii)Aldehydes A and B are structural isomers. State the type of structural isomerism shown by A and B.[1]
(a)(iii)Name A.[1]
(a)(iv)The complete reaction of propene with a 1:1 mixture of CO and H2 produces A and B only. The product mixture contains 96% A and 4% B. Calculate the mass of A produced in this reaction when 5.00 × 103 kg of propene is used. mass of A = kg[1]
(b)(i)A undergoes a nucleophilic addition reaction with a mixture of HCN and KCN, forming compound C. Complete the diagram to show the mechanism for this reaction. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. Draw the structure of the organic intermediate.[4]
(b)(ii)Table 3.1 shows information about three experiments involving B. Complete Table 3.1. [Table 3.1][3]
(b)(iii)B, C4H8O, is oxidised by acidified potassium manganate(VII). Complete the equation for this reaction. Use [O] to represent one atom of oxygen from the oxidising agent. C4H8O +[1]
(b)(iv)C is a chiral molecule. Circle any chiral centres in the structure of C shown in Fig. 3.2. [Fig. 3.2][1]
(c)When propene reacts with CO and an excess of H2, an alkane and a mixture of alcohols are formed instead. The alcohols are isomers of each other. Suggest the molecular formulae of the alkane and the alcohols that are formed under these conditions. molecular formula of alkane molecular formula of alcohols[2]
(d)(i)The reaction of ethene, C2H4, with a 1:1 mixture of CO and H₂ is shown in equation 1. equation 1 C2H4(g) + CO(g) + H2(g) ⇌ CH3CH2CHO(g) At atmospheric pressure a cobalt-based catalyst is used in this reaction. State and explain the effect of using a catalyst on this reaction.[2]
(d)(ii)Explain why the yield of CH3CH2CHO(g) increases when the overall pressure of the reaction mixture is increased.[1]
(d)(iii)Use the information in Table 3.2 to calculate the enthalpy change, ∆H, of the reaction in equation 1. equation 1 C2H4(g) + CO(g) + H2(g) ⇌ CH3CH2CHO(g) [Table 3.2] ∆H = kJmol⁻¹[2]
(d)(iv)The reaction mixture is cooled to collect CH3CH2CHO as a liquid. Identify all types of van der Waals' forces that are present between molecules of CH3CH2CHO.[1]

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 2023). The mark or mark type is shown in brackets.

[1] 3(a)(i) (a reaction where) two (or more) compounds / reagents / molecules form (only) one product
[1] 3(a)(ii) position(al isomerism)
[1] 3(a)(iii) butanal
[1] 3(a)(iv) 96% × (5000 / 42.0) × 72.0 = 8230 or 8229 (kg)
[1] 3(b)(i) curly arrow from lone pair on C of CN⁻ to C(δ+)
[1] 3(b)(i) correct dipole on C=O AND curly arrow from C=O bond to O(δ⁻)
[1] 3(b)(i) correct organic intermediate
[1] 3(b)(i) curly arrow from lone pair on alkoxide O(⁻) to H⁺ / H of HCN / H of H₂O (to reform the alcohol)
[1] 3(b)(ii) acidified K2Cr2O7
[1] 3(b)(ii) Tollens' reagent
[1] 3(b)(ii) no reaction
[1] 3(b)(iii) C4H8O + [O] → C4H8O2
[1] 3(b)(iv) Circle around the carbon bonded to OH, H, CN, and C3H7
[1] 3(c) alkane C3H8
[1] 3(c) alcohols C4H10O
[1] 3(d)(i) increases the rate of reaction
[1] 3(d)(i) by providing an alternative reaction pathway of lower Eₐ
[1] 3(d)(ii) equilibrium moves to right/products where fewer moles / smaller amount of gas
[1] 3(d)(iii) -187-(-111)-(+52)
[1] 3(d)(iii) = -128 (kJ mol⁻¹)
[1] 3(d)(iv) instantaneous dipole-induced dipole / id-id AND permanent dipole—permanent dipole / pd-pd