Crude Oil, Fractional Distillation and Hydrocarbons
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Crude oil is a mixture of mostly alkanes. Crude oil is separated into useful fractions by fractional distillation. Describe and explain how the mixture of alkanes is separated by fractional distillation. (3 marks)
• heat / evaporate the crude oil / change to gas or vapour • cool / condense (hydrocarbons) • at different temperatures / boiling points
The C5–C8 fraction has low supply and high market demand. Suggest three ways in which the oil industry could overcome this problem. (3 marks)
• use different / lighter crude oils • develop markets for low demand fractions • develop new techniques / equipment to use low demand fractions as fuels • cracking • convert low demand fractions to high demand fractions or bigger molecules to smaller molecules • develop alternative / bio fuels
What does unsaturated mean? (1 mark)
When it contains a(a carbon carbon) double (covalent) bond accept C = C accept alkene
Describe the link between the number of carbon atoms in an alkane molecule and its boiling point. (1 mark)
the greater the number of (carbon) atoms (in an alkane molecule) the greater its boiling point or vice versa
Crude oil is the source of many useful materials. Crude oil is separated into fractions by fractional distillation. Describe how the naphtha fraction separates from the other fractions. (2 marks)
• naphtha has a different / low(er) boiling point • condenses at a different temperature / height / place in the column / when it reaches its boiling point • different size of molecules
Describe how cracking is carried out. (2 marks)
• (hydrocarbon) heated / vapours - (passed over a) catalyst
Why does ethene have different chemical properties from decane and hexane? (2 marks)
ethene is unsaturated or decane and hexane / they are saturated ethene has a double (carbon carbon) bond or decane and hexane have only single (carbon carbon) bonds accept decane and hexane are alkanes or ethene is an alkene / CnH2n
How does the number of carbon atoms in a hydrocarbon affect its boiling point? (1 mark)
The greater the number (of carbon atoms), the higher its boiling point
Describe how crude oil is separated into fractions. (2 marks)
vaporise / evaporate different condensing points / temperatures allow boil for vaporise accept condense at different levels ignore different size molecules or different densities allow boils at different temperatures and condenses for 2 marks
Describe how cracking is carried out. (2 marks)
Boil / vaporise / evaporate (passed over) a catalyst
Alkanes, such as butane (C4H10), do not form polymers. Alkenes, such as ethene (C2H4), do form polymers. Explain these statements. (2 marks)
• alkanes / butane (molecules) do not have a (carbon carbon) double bond / are saturated / have (carbon carbon) single bonds • alkenes / ethene (molecules) have (carbon carbon) double bonds or are unsaturated • alkenes / ethene molecules are able to bond to other molecules
Explain how crude oil is separated into fractions. You should use the words evaporated and condensed in your answer. (3 marks)
• crude oil / it is evaporated / vaporised • vapours / gases / fractions cool and condense • (different) vapours / gases / fractions (condense) at different temperatures ignore heated accept (different) vapours / gases/ fractions have different boiling points
Describe how fuel oil is broken down into smaller, more useful molecules such as gasoline (petrol). (2 marks)
any two from: • cracking / (thermal) decomposition • heat / vaporise • catalyst
Explain how carbon monoxide is formed. (2 marks)
by incomplete / partial combustion (of the fuel) insufficient oxygen / air (to burn fuel)
Why does crude oil need to be fractionally distilled? (1 mark)
it is a mixture (of hydrocarbons) or contains hydrocarbons with different boiling points
Describe how cracking is done. (2 marks)
heat / vaporise catalyst
How are hydrocarbons cracked? (2 marks)
heat / high temperature / hot / vaporise catalyst
Describe a test to distinguish between an alkane and alkene and give the result of the test. (2 marks)
add bromine (water) alkene will decolourise the solutions or alkane will not decolourise the solutions