Question 1 Medium
Name the two types of product made when a long alkane is cracked.
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Answer: a shorter alkane and an alkene
- One has only single bonds.
- The other has a double bond.
Crude oil, hydrocarbons and cracking: GCSE Combined Science Chemistry practice questions
A second set of questions on crude oil, hydrocarbons and cracking. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
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Question 2 Medium
Which fraction is used as aircraft fuel?
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Answer: kerosene
- It has a medium chain length.
- It is kerosene.
Question 3 Medium
What is the formula of the alkane with 12 carbon atoms?
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Answer: C₁₂H₂₆
- Hydrogen atoms = 2 × 12 + 2.
- 2 × 12 + 2 = 26.
Question 4 Medium
Name the gas that is made, as well as water, when a hydrocarbon burns completely.
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Answer: carbon dioxide
- Complete combustion needs plenty of oxygen.
- The carbon in the hydrocarbon is fully oxidised.
Question 5 Hard
Balance the equation: C₁₀H₂₂ → C₈H₁₈ + C₂H₄. State the total number of hydrogen atoms on the right.
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Answer: 22
- C₈H₁₈ has 18 H and C₂H₄ has 4 H.
- 18 + 4 = 22.
Question 6 Hard
Complete the equation for cracking: C₁₂H₂₆ → C₈H₁₈ + __. Give the formula of the missing product.
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Answer: C₄H₈
- Carbon: 12 − 8 = 4.
- Hydrogen: 26 − 18 = 8, so the missing product is C₄H₈.
Question 7 Hard
Explain why the boiling points of alkanes increase as the chain gets longer.
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Answer: the intermolecular forces are stronger so more energy is needed
- Longer molecules have stronger intermolecular forces.
- More energy is needed to separate them.
Question 8 Hard
Give one reason why a gas appliance must be properly ventilated.
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Answer: to stop incomplete combustion making carbon monoxide
- A lack of oxygen causes incomplete combustion.
- Carbon monoxide is toxic.
Question 9 Medium
Are petrol and diesel renewable or non-renewable fuels?
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Answer: non-renewable
- They come from crude oil, which took millions of years to form.
- So they are non-renewable.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is a hydrocarbon?
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A compound made of hydrogen and carbon only.
Check 2
What is crude oil?
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A mixture of hydrocarbons, mostly alkanes.
Check 3
How did crude oil form?
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From ancient marine organisms buried under mud for millions of years.
Check 4
What is the general formula of alkanes?
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CₙH₂ₙ₊₂.
Check 5
What does saturated mean?
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Only single bonds between carbon atoms.
Check 6
How does fractional distillation separate crude oil?
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By different boiling points in a column that is hotter at the bottom.
Check 7
Which fractions have the lowest boiling points?
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Refinery gases, collected at the top.
Check 8
What is bitumen used for?
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Surfacing roads.
Check 9
What is kerosene used for?
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Aircraft fuel.
Check 10
How does viscosity change with chain length?
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It increases.
Check 11
How does flammability change with chain length?
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It decreases.
Check 12
What are the products of complete combustion of a hydrocarbon?
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Carbon dioxide and water.
Check 13
Which toxic gas can form in incomplete combustion?
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Carbon monoxide.
Check 14
What is cracking?
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Breaking long hydrocarbon molecules into smaller ones.
Check 15
What catalyst is used for catalytic cracking?
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Aluminium oxide or a zeolite.
Check 16
Why is cracking done?
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Demand for small hydrocarbons is greater than supply.
Check 17
What type of hydrocarbon is made by cracking along with an alkane?
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An alkene.
Check 18
What is a fraction in crude oil?
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A group of hydrocarbons with similar boiling points.
Check 19
What does finite mean for crude oil?
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It will run out, because it is used faster than it forms.
Check 20
What is the formula of methane?
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CH₄.
Check 21
What is the formula of propane?
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C₃H₈.
Check 22
What is viscosity?
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How thick a liquid is, and how slowly it flows.
Check 23
What does volatile mean?
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It evaporates easily.
Check 24
Which fraction fuels lorries and trains?
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Diesel oil.
Check 25
What is a fractionating column?
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A tall tower that is hot at the bottom and cooler at the top.
Check 26
What can form when a fuel burns in too little oxygen?
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Carbon monoxide or carbon (soot), as well as water.
Check 27
What type of reaction is cracking?
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Thermal decomposition.
Check 28
Why are fossil fuels non-renewable?
Show answer
They take millions of years to form and are used much faster than they are made.
Check 29
Name three fuels obtained from crude oil.
Show answer
Petrol, kerosene and diesel oil.
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