A-LevelChemistryAnalytical techniques9701/22 · Oct/Nov 2022 · Q322 Marks

Organic compounds can be distinguished using chemical tests and analytical techniques. [Table 3.1]

(a)(i)Complete Table 3.1 to: • identify a reagent which can distinguish between the compounds in each pair • give the positive result of the chemical test and identify which compound shows this result. Use a different reagent for each test.[8]
(a)(ii)A1 and A2 are structural isomers. Define structural isomers.[1]
(a)(iii)Give the systematic name of B2.[1]
(a)(iv)Deduce the molecular formula of D1.[1]
(b)(i)D2 forms polymer Z when heated gently. Identify the type of polymer that forms from D2.[1]
(b)(ii)Draw one repeat unit of polymer Z.[2]
(c)(i)Organic compound E contains three carbon atoms. E reacts with cold dilute acidified KMnO4(aq) to form a single compound F with Mᵣ = 154.9. Fig. 3.1 shows the infrared spectrum of E. Fig. 3.2 shows the infrared spectrum of F. Use the two infrared spectra and Table 3.2 to identify the functional group present only in E. Explain your answer, referring only to absorptions at frequencies greater than 1500 cm⁻¹.[1]
(c)(ii)Use the infrared spectrum of F to identify the functional group formed when E reacts with cold dilute acidified KMnO4(aq). Explain your answer, referring only to absorptions at frequencies greater than 1500 cm⁻¹.[1]
(c)(iii)The mass spectrum of E shows a molecular ion peak and an M+2 peak of approximately equal abundance at m/e = 120 and 122. Deduce the relative molecular mass, Mᵣ, of E.[1]
(c)(iv)Use the information in 3(c) to suggest a structure for E.[1]
(c)(v)Complete the equation for the reaction of E with cold dilute acidified KMnO4(aq) to form F. In the equation, [O] represents cold dilute acidified KMnO4(aq). H₂O + [O] + ________ → ________[1]
(d)C2 can be synthesised using A1 as a single organic reactant. Devise a multi-step synthetic route to form C2 from A1. Identify relevant reagents and conditions, and state the organic products of each step. [Diagrams of A1 and C2][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 2022). The mark or mark type is shown in brackets.

[2] M1 Tollens' OR Fehling's OR K2Cr2O7 OR KMnO4 A1 gives silver mirror OR brick-red ppt OR (orange solution) turns green OR (purple solution) turns colourless
[2] OR alkaline I2(aq) with M3 alkaline I2(aq) M4 B1 gives yellow ppt
[2] M5 2,4-DNPH M6 C1 gives red/orange/yellow ppt
[2] M7 Br2(aq) M8 D2 turns it (orange to) colourless
[1] molecules with the same molecular formula AND different structural formulae owtte
[1] pentan-3-one
[1] molecular formula C5H10O
[1] addition
[1] M1 correct carbon backbone of one repeat unit including 'dangling' bonds
[1] M2 rest of structure correct
[1] C=C (bond) / alkene AND (absorption within) 1500–1680 cm⁻¹ (present in E's IR spectrum only)
[1] hydroxyl / alcohol AND (broad absorption within) 3200–3650 cm⁻¹ (present in F's IR spectrum only)
[1] 120.9/121
[1] (structure: CH2=CH-CH2Br)
[1] (1)H₂O + (1)[O] + C3H5Br → C3H7BrO2
[1] M1 one portion of A1: NaBH₄ AND → propan-1-ol / CH₃(CH₂)₂OH
[1] M2 second portion of A1: acidified K₂Cr₂O₇ AND → propanoic acid / C₂H₅CO₂H
[1] M3 two products: conc(entrated mineral) acid / H⁺ / H₂SO₄ (catalyst)