Paper 4 Organic Chemistry Structured Practice
5 structured exam questions on organic chemistry for IGCSE Chemistry Paper 4. Covers homologous series, isomerism, reactions of alkenes and alcohols, polymers, and esters. Total: 26 marks.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Five structured questions in the style of IGCSE Chemistry Paper 4, totalling 26 marks. Write your answers in full before checking the mark scheme.
Question 1 (5 marks)
Ethene (C₂H₄) and ethane (C₂H₆) are both hydrocarbons.
(a) Define the term hydrocarbon. [1]
(b) State the homologous series to which each belongs. [2]
(c) Describe a chemical test to distinguish between ethene and ethane. State the reagent, the method, and the results for both gases. [2]
Mark scheme
(a) A compound containing hydrogen and carbon atoms only [1].
(b) Ethene: alkenes [1]. Ethane: alkanes [1].
(c) Add bromine water (orange/brown) to each gas and shake [1]. Ethene decolourises the bromine water (addition reaction across the C=C bond). Ethane does not react / the bromine water stays orange [1].
Total: 5 marks
Question 2 (6 marks)
Ethanol (C₂H₅OH) can be manufactured by two methods.
(a) Describe how ethanol is produced by fermentation. State the starting material, the conditions needed, and the equation. [3]
(b) Describe how ethanol is produced by the hydration of ethene. State the conditions and the equation. [2]
(c) State one advantage of fermentation over hydration. [1]
Mark scheme
(a) Glucose / sugar solution is mixed with yeast [1]. The mixture is kept at 25-40 degC in the absence of air / anaerobic conditions [1]. C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ [1].
(b) Ethene is reacted with steam at high temperature (about 300 degC) and high pressure (about 60-70 atm) in the presence of a phosphoric acid catalyst [1]. C₂H₄ + H₂O → C₂H₅OH [1].
(c) Fermentation uses a renewable resource (sugar from plants) whereas hydration uses ethene from crude oil, which is non-renewable [1]. Accept: fermentation uses lower temperatures, so less energy is needed.
Total: 6 marks
Question 3 (5 marks)
Butane (C₄H₁₀) has structural isomers.
(a) Define the term isomer. [1]
(b) Draw the displayed (structural) formulae of the two isomers of butane. Name each isomer. [4]
Mark scheme
(a) Isomers are compounds with the same molecular formula but different structural formulae / different arrangements of atoms [1].
(b) Isomer 1: Butane --- a straight chain of 4 carbon atoms (CH₃-CH₂-CH₂-CH₃) with correct number of hydrogen atoms shown [2].
Isomer 2: Methylpropane / 2-methylpropane --- a chain of 3 carbon atoms with a CH₃ branch on the middle carbon (CH₃-CH(CH₃)-CH₃) with correct number of hydrogen atoms shown [2].
Total: 5 marks
Question 4 (5 marks)
Poly(ethene) and nylon are both polymers.
(a) State what is meant by the term polymer. [1]
(b) Poly(ethene) is made by addition polymerisation. Name the monomer and draw the repeating unit of poly(ethene). [2]
(c) State one difference between addition polymerisation and condensation polymerisation. [1]
(d) State one environmental problem caused by disposal of addition polymers such as poly(ethene). [1]
Mark scheme
(a) A polymer is a very long chain molecule made by joining together many small molecules (monomers) [1].
(b) Monomer: ethene (C₂H₄) [1]. Repeating unit: -CH₂-CH₂- (shown with extending bonds at each end) [1].
(c) Addition polymerisation produces only the polymer (one product). Condensation polymerisation produces the polymer and a small molecule (such as water or HCl) as a by-product [1].
(d) Addition polymers are non-biodegradable, so they persist in landfill for hundreds of years / take up space in landfill / cause litter and harm wildlife [1].
Total: 5 marks
Question 5 (5 marks)
Ethyl ethanoate is an ester.
(a) Name the alcohol and the carboxylic acid needed to make ethyl ethanoate. [2]
(b) Write the equation for this esterification reaction. [1]
(c) State the catalyst used for esterification. [1]
(d) State one use of esters. [1]
Mark scheme
(a) Alcohol: ethanol [1]. Carboxylic acid: ethanoic acid [1].
(b) CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O [1] (Accept: ethanoic acid + ethanol → ethyl ethanoate + water)
(c) Concentrated sulfuric acid (as a catalyst) [1].
(d) Any one from: solvents / flavourings / perfumes / fragrances [1].
Total: 5 marks
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