(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
Structure Q contains the -COOH functional group characteristic of carboxylic acids.
(a)(ii) Ans: S
Structure S is an alkane (C₅H₁₂), belonging to the same homologous series as ethane (C₂H₆).
(a)(iii) Ans: R
Structure R is an alkene (C₃H₆) which reacts with bromine water, causing decolorization.
(a)(iv) Ans: C₄H₈O₂
Q has 4 carbon atoms, 8 hydrogen atoms (accounting for the double bond O), and 2 oxygen atoms.
(b)(i) Ans: alkenes
Cracking produces both shorter alkanes and unsaturated alkenes as byproducts.
(b)(ii) Ans: breakdown of a compound (1)
using heat / by heat (1)
Thermal decomposition refers to the chemical breakdown of substances when heated, without other reactants.
(c) Ans:
naphtha → making chemicals
lubricating fraction → waxes and polishes
kerosene → jet fuel
Naphtha’s low boiling range makes it ideal for chemical feedstocks, while lubricating fractions have high viscosity for waxes, and kerosene’s medium chain length suits jet engines.
(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 (but-1-ene) is unsaturated (has C=C bond) and reacts with bromine water, causing decolorization.
(a)(ii) Ans: D
Compound D (butan-1-ol) contains the -OH functional group characteristic of alcohols.
(a)(iii) Ans: C
Compound C has a carbon-carbon double bond (C=C), making it unsaturated.
(a)(iv) Ans: E
Compound E (butane) is an alkane, same homologous series as ethane (both have single C-C bonds).
(b) Ans: fractional distillation
Petroleum is separated based on different boiling points of components using fractional distillation.
(c) Ans:
Refinery gas: domestic heating/cooking
Gasoline: fuel for cars/vehicles
Waxes: lubrication/candles
(d)(i) Ans: Breaking long-chain hydrocarbons into shorter chains
Cracking converts less useful long hydrocarbons into more valuable shorter ones.
(d)(ii) Ans: High temperature (400-900°C) and catalyst
Cracking requires heat to break bonds and a catalyst (e.g., aluminum oxide) to speed up the reaction.