Paper 2 Organic Chemistry MCQ Practice
10 multiple-choice questions on organic chemistry for IGCSE Chemistry Paper 2. Covers homologous series, alkanes, alkenes, alcohols, carboxylic acids, esters, and polymers.
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.
Ten multiple-choice questions in the style of IGCSE Chemistry Paper 2. Choose the best answer for each, then check the mark scheme.
Question 1
What is the general formula for alkanes?
A. CₙH₂ₙ B. CₙH₂ₙ₊₂ C. CₙH₂ₙ₋₂ D. CₙH₂ₙ₊₁OH
Answer
B
The general formula for alkanes is CₙH₂ₙ₊₂. Alkanes are saturated hydrocarbons with only single C-C and C-H bonds. For example, methane (n=1) is CH₄, ethane (n=2) is C₂H₆, propane (n=3) is C₃H₈. Option A is the general formula for alkenes.
Question 2
Which test distinguishes an alkene from an alkane?
A. Adding litmus paper B. Adding bromine water --- it decolourises with an alkene C. Burning the substance D. Adding universal indicator
Answer
B
Bromine water (orange/brown) rapidly decolourises when shaken with an alkene because the bromine adds across the C=C double bond (an addition reaction). Alkanes do not react with bromine water under these conditions, so the orange colour remains. This is the standard test for unsaturation.
Question 3
Ethanol can be produced by fermentation. Which conditions are needed?
A. Yeast, high temperature (above 80 degC), glucose B. Yeast, warm temperature (25-40 degC), glucose C. Concentrated sulfuric acid, high pressure, ethene D. Steam, high temperature, catalyst
Answer
B
Fermentation requires glucose, yeast (a biological catalyst), and a warm temperature (about 25-40 degC). If the temperature is too high, the enzymes in yeast are denatured and the reaction stops. Options C and D describe the industrial hydration of ethene, not fermentation.
Question 4
What is the functional group of carboxylic acids?
A. -OH B. -COOH C. C=C D. -COO-
Answer
B
The functional group of carboxylic acids is -COOH (the carboxyl group). The -OH group is the functional group of alcohols. The C=C double bond is the functional group of alkenes. The -COO- group is the ester linkage.
Question 5
Fractional distillation of crude oil separates the hydrocarbons based on differences in their:
A. colour B. density C. boiling point D. flammability
Answer
C
Fractional distillation separates crude oil into fractions based on differences in boiling point. The crude oil is heated and the vapours rise up the fractionating column. Hydrocarbons with lower boiling points (shorter chains) rise higher before condensing. Longer-chain hydrocarbons condense lower in the column.
Question 6
Which molecule is an ester?
A. CH₃COOH B. CH₃CH₂OH C. CH₃COOCH₃ D. CH₃CH₂CH₃
Answer
C
CH₃COOCH₃ (methyl ethanoate) is an ester. Esters are formed from a carboxylic acid and an alcohol. They contain the -COO- linkage. CH₃COOH is ethanoic acid, CH₃CH₂OH is ethanol, and CH₃CH₂CH₃ is propane.
Question 7
Poly(ethene) is formed by:
A. condensation polymerisation of ethanol B. addition polymerisation of ethene C. hydration of ethene D. cracking of ethene
Answer
B
Poly(ethene) is formed by addition polymerisation of many ethene monomers. The C=C double bonds in ethene open up and the molecules join together to form a long chain. No other product is formed. The repeating unit is -CH₂-CH₂-.
Question 8
As the chain length of alkanes increases, the boiling point:
A. decreases B. remains constant C. increases D. first increases then decreases
Answer
C
As alkane chain length increases, boiling point increases because the intermolecular forces between larger molecules are stronger. More energy is needed to separate the molecules. This is why methane (1 carbon) is a gas at room temperature, while octane (8 carbons) is a liquid and longer-chain alkanes are solids.
Question 9
What type of reaction occurs when ethene reacts with steam in the presence of a catalyst?
A. Combustion B. Substitution C. Addition D. Elimination
Answer
C
When ethene reacts with steam, water adds across the C=C double bond to form ethanol: C₂H₄ + H₂O → C₂H₅OH. This is an addition reaction (also called hydration). The double bond opens and both parts of the water molecule (H and OH) add to the two carbon atoms. Only one product is formed.
Question 10
Cracking is used to:
A. join small molecules into larger ones B. break down large hydrocarbon molecules into smaller, more useful ones C. separate crude oil into fractions D. remove sulfur from hydrocarbons
Answer
B
Cracking breaks down large, less useful hydrocarbon molecules into smaller, more useful ones (such as petrol-range alkanes and alkenes). Cracking requires high temperature and a catalyst (catalytic cracking) or high temperature and steam (steam cracking). It produces at least one alkene, which is important for making polymers.
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