AQA GCSE Chemistry (8462), Higher tier · Organic chemistry › Carbon compounds as fuels and feedstock
Practise Crude oil, hydrocarbons and alkanes. 12 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Crude oil is a finite resource found in rocks. What is meant by a finite resource?
A resource that will run out because it is not being replaced.
The general formula of the alkanes is CnH2n+2. Give the formula of the alkane with 7 carbon atoms.
C7H16
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Crude oil is a finite resource found in rocks.
(a) What is meant by a finite resource?[1]
(b) Crude oil is the remains of an ancient biomass. What did this biomass mainly consist of? Tick (✓) one box.[1]
Plankton
Dinosaurs
Trees
Volcanic ash
(c) Most of the compounds in crude oil are hydrocarbons. What is a hydrocarbon?[2]
(d) Name the alkane with the formula C3H8.[1]
Show the answer and mark scheme
(a)Answer: A resource that will run out because it is not being replaced.
it will run out / it is not being made (or replaced) as fast as it is used
(b)Answer: Plankton
(c)Answer: A compound made of hydrogen and carbon atoms only.
a compound / molecule containing hydrogen and carbon (atoms)
only
(d)Answer: Propane
propane
Question 2Medium3 marks
A technician tests an unknown colourless liquid taken from crude oil processing.
A few drops of the liquid are added to bromine water: the bromine water stays orange.
A small sample is burned: it burns with a clean, non-smoky blue flame.
(a) What does the bromine water result show about the liquid?[1]
(b) Suggest what type of hydrocarbon this liquid is, and suggest whether it has a small or large number of carbon atoms. Give a reason for your suggestion about chain length.[2]
Show the answer and mark scheme
(a)Answer: It is saturated (it does not contain a carbon–carbon double bond).
the liquid is saturated / does not contain a C=C double bond (it is not an alkene)
(b)Answer: An alkane, probably with a small number of carbon atoms: a clean, non-smoky flame suggests complete combustion, which is typical of shorter-chain hydrocarbons.
an alkane (a saturated hydrocarbon)
a small number of carbon atoms (short chain), because it burns with a clean, non-smoky flame (long-chain hydrocarbons burn with smokier flames)
Question 3Hard6 marks
The alkanes are a homologous series with the general formula CnH2n+2. Relative atomic masses (Ar): H = 1 C = 12
(a) An alkane has a relative formula mass (Mr) of 114. Determine the molecular formula of the alkane.[3]
(b) Calculate the percentage by mass of carbon in this alkane. Give your answer to 3 significant figures.[2]
(c) How many hydrogen atoms are there in one molecule of the alkane with 20 carbon atoms?[1]