(a) The structures of four organic compounds, P, Q, R and S, are shown.
Answer the following questions about these structures. Each structure may be used once, more than once or not at all.
(i) State which structure, P, Q, R or S, has a carboxylic acid functional group. [1]
(ii) State which structure, P, Q, R or S, is in the same homologous series as ethane. [1]
(iii) State which structure, P, Q, R or S, decolourises aqueous bromine. [1]
(iv) Deduce the molecular formula of structure Q to show the number of carbon, hydrogen and oxygen atoms. [1]
(b) Structure S is produced by cracking petroleum fractions.
(i) Complete the sentence using a word from the list.
acids alkenes alcohols nitrogen
During cracking, long-chain alkanes are converted to shorter chain alkanes and ________. [1]
(ii) Cracking is an example of thermal decomposition.
State the meaning of the term thermal decomposition. [2]
(c) Link each petroleum fraction on the left to its use on the right.
The first one has been done for you.
▶️ Answer/Explanation
(a)(i) Ans: Q
Q has the −COOH group, which is characteristic of carboxylic acids.
(a)(ii) Ans: S
S is an alkane (C₅H₁₂), same homologous series as ethane (C₂H₆).
(a)(iii) Ans: R
R is an alkene (C₄H₈), which decolourises bromine water due to its C=C double bond.
(a)(iv) Ans: C₄H₈O₂
Q has 4 carbon atoms, 8 hydrogen atoms, and 2 oxygen atoms.
(b)(i) Ans: alkenes
Cracking produces shorter alkanes and alkenes (e.g., ethene, propene).
(b)(ii) Ans:
Thermal decomposition is the breakdown of a compound (1) using heat (1).
(c) Ans:
Naphtha → making chemicals (1)
Lubricating fraction → waxes and polishes (1)
Kerosene → jet fuel (1).
Award 2 marks for all correct, 1 mark for 1–2 correct.
(a) The structures of four organic compounds, C, D, E and F, are shown.
Answer the following questions about these compounds.
Each compound may be used once, more than once or not at all.
State which compound, C, D, E or F:
(i) decolourises aqueous bromine [1]
(ii) is an alcohol [1]
(iii) is unsaturated [1]
(iv) is in the same homologous series as ethane. [1]
(b) Petroleum is a mixture of hydrocarbons which can be separated into fractions with different boiling points.
Name the method used to separate these fractions.[1]
(c) Complete the table to show the name and uses of some petroleum fractions.[3]
(d) Some hydrocarbons are formed by the process of cracking.
(i) State the meaning of the term cracking.[2]
(ii) Describe the conditions needed for cracking.[2]
▶️ Answer/Explanation
(a)(i) Ans: C
Compound C (ethene) has a C=C double bond, which reacts with bromine, decolourising it.
(a)(ii) Ans: D
Compound D (ethanol) contains an –OH functional group, characteristic of alcohols.
(a)(iii) Ans: C
Compound C is unsaturated due to the presence of a C=C double bond.
(a)(iv) Ans: E
Compound E (propane) is an alkane, the same homologous series as ethane.
(b) Ans: Fractional distillation
Petroleum is separated into fractions based on boiling points using fractional distillation.
(c) Ans:
Refinery gas: Heating/cooking
Gasoline: Fuel for cars
Waxes: Lubricants
(d)(i) Ans: Breakdown of long-chain hydrocarbons into shorter chains.
Cracking converts large hydrocarbons into smaller, more useful molecules.
(d)(ii) Ans: High temperature (≈600°C) and a catalyst (e.g., alumina).
These conditions break C–C bonds in long-chain hydrocarbons efficiently.