Alkanes (Edexcel AS Chemistry)

Exam Questions

28 mins4 questions

1a4 marks

Some alkanes are used as fuels for transport. Crude oil, which is a mixture of hydrocarbons, is the major source of these alkanes. Crude oil is processed by fractional distillation, cracking and reforming.

Fractional distillation produces fractions which contain molecules of a similar boiling temperature. Molecules containing six carbon atoms are found in both the petrol fraction and the higher boiling kerosene fraction.

Identify, by name or structural formula, the unbranched alkane with six carbon atoms found in kerosene.

(1)

ii)

Explain why isomers of the alkane in (a)(i) have lower boiling temperatures and so are found in the petrol fraction.

(3)

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1b3 marks

During cracking, carbon to carbon bonds are broken.

Explain the two major reasons for cracking hydrocarbons.

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1c1 mark

Which of the following changes to the proportions of organic molecules within a fraction results from the reforming process?

		Proportion of branched chain alkanes	Proportion of cyclic hydrocarbons
☐	A	decrease	decrease
☐	B	decrease	increase
☐	C	increase	decrease
☐	D	increase	increase

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☐	A	carbon particulates
☐	B	oxides of nitrogen
☐	C	oxides of sulfur
☐	D	unburnt hydrocarbons

☐	A	elimination
☐	B	hydrogenation
☐	C	isomerisation
☐	D	reforming

☐	A	C₁₀H₂₂
☐	B	C₁₀H₂₀
☐	C	C₁₀H₁₈
☐	D	C₁₀H₁₆

☐	A	4-ethyloctane
☐	B	5-ethyloctane
☐	C	3-propylheptane
☐	D	5-propylheptane

☐	A	substitution
☐	B	reforming
☐	C	fractional distillation
☐	D	cracking

☐	A	heterolytic bond fission to form free radicals
☐	B	heterolytic bond fission to form ions
☐	C	homolytic bond fission to form free radicals
☐	D	homolytic bond fission to form ions

☐	A	bromine is very unreactive
☐	B	a gaseous reactant always gives a low yield
☐	C	the reaction is very slow
☐	D	the reaction produces a mixture of organic products