Organic chemistry marking scheme

This is the marking scheme for quiz: C11 - Organic Chemistry Quiz
Topic Guide: C11 - Organic Chemistry

Total marks: 22

Accept equivalent displayed or structural formulae where bonds and atom connections are unambiguous.

Section A: Multiple choice (5 marks)

Q1 (1 mark)

B — Alkenes have general formula $C_nH_{2n}$. [1]

Q2 (1 mark)

C — Volatility increases from the bottom to the top of the column. [1]

Q3 (1 mark)

A — Ultraviolet light is required for substitution of methane with chlorine. [1]

Q4 (1 mark)

B — Orange-brown aqueous bromine becomes colourless. [1]

Q5 (1 mark)

D — Poly(ethene) forms from ethene by addition polymerisation. [1]

Section B: Short answer (17 marks)

Q6 (2 marks)

  1. Ethene: CH2=CH2. [1]
  2. Ethanol: CH3CH2OH or C2H5OH. [1]

Q7 (3 marks)

  • Structural isomers have the same molecular formula but different structural formulae. [1]
  • Members of a homologous series have the same functional group or general formula. [1]
  • Successive members differ by a –CH2– unit, or they have similar chemical properties and a gradual trend in physical properties. [1]

Q8 (3 marks)

  • Petroleum is heated so that it vaporises and the vapours enter a fractionating column. [1]
  • Different hydrocarbons condense at different heights because they have different boiling points. [1]
  • Any two valid trends from bottom to top: chain length decreases; boiling point decreases; volatility increases; viscosity decreases. [1]

Q9 (3 marks)

  1. Poly(propene) repeat unit: $[-CH_2-CH(CH_3)-]_n$. [1]
  2. Addition polymerisation. [1]
  3. No small molecule is produced. [1]

Q10 (6 marks)

  1. Methane: CH4; ethene: CH2=CH2. [2]
  2. Methane is saturated; ethene is unsaturated. [1]
  3. Ethene decolourises orange-brown aqueous bromine to colourless; methane does not decolourise it under these conditions. [1]
  4. $CH_2{=}CH_2 + Br_2 \rightarrow CH_2BrCH_2Br$. [2]
    • Correct reactants and product: [1]
    • Balanced equation: [1]

Q11 (6 marks)

  1. Fermentation uses yeast, glucose solution, $25$–$35\ ^\circ\mathrm{C}$, and no oxygen. Award the mark for the complete relevant set of conditions. [1]
  2. $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$. [1]
  3. $C_2H_4 + H_2O \rightleftharpoons C_2H_5OH$. [1]
  4. $300\ ^\circ\mathrm{C}$, $6000\ \mathrm{kPa}$, and an acid catalyst. [1]
  5. One mark for each valid advantage:
    • Fermentation uses renewable plant material or requires low temperature and pressure. [1]
    • Catalytic addition is fast, continuous, or produces a more concentrated product. [1]