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Question 1
Crude oil is a mixture of many hydrocarbons which can be separated by fractional distillation to produce a number of fractions with different boiling points. |
a) | Explain why hydrocarbons in crude oil have different boiling points.
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b) | Explain why, after separation of the fractions, some hydrocarbons are processed further by cracking.
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c) | Decane, C10H22, is an alkane which undergoes cracking to produce two molecules of ethene and one other hydrocarbon. Write an equation to represent this process.
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d) | Alkanes are a homologous series consisting of saturated molecules. Explain the meaning of the term saturated.
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e) | The bond angle around each carbon atom in an alkane is 109.5 °. State and explain the shape around each carbon atom.
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Question 2
Alkanes can react with halogens to form halogenoalkanes. |
a) | State the name of the mechanism for this reaction and the condition needed for this reaction to occur.
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b) | Methane and bromine can react to form bromomethane. Write an equation for the initiation step in this reaction and explain why this is an example of homolytic fission.
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c) | The first equation in the propagation step can be written as shown below. CH4 + Br• ➔ •CH3 + HBr Write an equation for the second propagation step.
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d) | Write an equation for the termination step that results in the formation of ethane, C2H6.
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Question 3
The alkanes hexane and 2,2-dimethylbutane are structural isomers with the molecular formula C6H14. |
a) | Draw the skeletal formula of both alkanes.
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b) | Explain why 2,2-dimethylbutane has a lower boiling point than hexane.
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c) | Write an equation for the complete combustion of hexane.
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d) | State under what conditions incomplete combustion of hexane would occur and write an equation for the reaction.
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Question 4
Nonane is an alkane with the molecular formula C9H20. It can be used as a fuel in jet engines or cracked to form other products. |
a) | State the general formula of the alkanes.
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b) | Write an equation to show the complete combustion of nonane.
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c) | A structural isomer of nonane is shown below. Give the name of this isomer.
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d) | Combustion in jet engines produces pollutants such as NO and CO. Explain how these pollutants are formed in internal combustion engines.
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e) | Explain why nonane has a higher boiling point than the structural isomer shown in part c).
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Question 5
The table below shows the boiling points of some saturated hydrocarbons. |
a) | Explain the meaning of the term hydrocarbon.
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b) | State and explain the trend in boiling points shown in the table.
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c) | All of the alkanes in the table react with halogens in the presence of ultraviolet light to form halogenoalkanes. Name the mechanism for this reaction.
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d) | Write two equations for the propagation step of this reaction between hexane, C6H14, and chlorine.
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Question 6
Halogenoalkanes have many uses, including as solvents and refrigerants. Bromoethane is formed from the reaction between ethane and bromine in the presence of ultraviolet light. |
a) | Write an overall equation for the reaction between ethane and bromine to form bromoethane and one other product.
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b) | Write an equation for the initiation step of this reaction.
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c) | The first equation in the propagation step is shown below. C2H6 + Br• ➔ •C2H5 + HBr Write an equation for the second propagation step.
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d) | Write a termination step for this reaction, resulting in the formation of butane.
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Question 7
This question is about the reactions of alkanes. Alkanes can be used as fuels. |
a) | Write a balanced equation for the combustion of octane (C8H18) in excess oxygen.
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b) | Combustion of 45.6 g of octane produced 3.00 moles of CO2. Show that this combustion was incomplete.
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c) | Alkanes react in free radical substitution reactions to form halogenoalkanes. Write two propagation steps for the reaction between propane and chlorine to form 2-chloropropane.
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Question 8
The alkane with a molecular formula of C8H18 has several structural isomers. The structure of one of these isomers is shown below. |
a) | Draw the skeletal formula of the isomer shown in the diagram above.
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b) | Under certain conditions, C8H18 reacts with chlorine to form C8H17Cl. Write an equation for the initiation step of this reaction, and state the conditions necessary for the reaction to occur.
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c) | Write an equation for the incomplete combustion of C8H18 to produce CO as the only carbon-containing product.
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d) | Catalytic converters are used to remove the toxic gases NO and CO produced when alkanes burn in combustion engines. Write an equation for a reaction between these two gases that occurs in a catalytic converter, and identify a metal that could be used as a catalyst in the reaction.
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Question 9
Free radical substitution reactions can occur between alkanes and halogens in the presence of UV light. |
a) | Classify each of the following equations as initiation, propagation or termination by ticking the appropriate box in the table below.
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b) | Which of the following equations represents a propagation step in free radical substitution? A •CH2Cl + Cl• ➔ CH2Cl2 B Cl2 ➔ 2Cl• C •C2H5 + •C2H5 ➔ C4H10 D CH3Cl + Cl• ➔ •CH2Cl + HCl
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c) | Which of the following species would not be formed in the free radical substitution of methane and bromine? A HBr B Br• C CH3Br D H•
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Question 10
Alkanes are saturated hydrocarbons which can be used as fuels. |
a) | Draw the skeletal formula of the alkane 2,3,3-trimethylpentane.
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b) | Write an equation for the complete combustion of dodecane.
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c) | Write an equation for the incomplete combustion of C11H24 to produce only H2O and a toxic gas.
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d) | Cracking of an alkane X produces one molecule of propene and one molecule of hexane. Deduce the molecular formula of alkane X and write an equation for the cracking process.
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