Alkanes - exam practice
Alkanes
Question 1 of 11
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.
Explain why hydrocarbons in crude oil have different boiling points.
Outline the key features of fractional distillation that enable crude oil to be separated into fractions.
Explain why, after separation of the fractions, some hydrocarbons are processed further by cracking.
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.
Alkanes are a homologous series consisting of saturated molecules.
Explain the meaning of the term saturated.
The bond angle around each carbon atom in an alkane is 109.5 °.
State and explain the shape around each carbon atom.
Alkanes can react with halogens to form halogenoalkanes.
State the name of the mechanism for this reaction and the condition needed for this reaction to occur.
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.
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.
Write an equation for the termination step that results in the formation of ethane, C2H6.
The alkanes hexane and 2,2-dimethylbutane are structural isomers with the molecular formula C6H14.
Draw the skeletal formula of both alkanes.
Explain why 2,2-dimethylbutane has a lower boiling point than hexane.
Write an equation for the complete combustion of hexane.
State under what conditions incomplete combustion of hexane would occur and write an equation for the reaction.
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.
State the general formula of the alkanes.
Write an equation to show the complete combustion of nonane.
A structural isomer of nonane is shown below.
Give the name of this isomer.
Combustion in jet engines produces pollutants such as NO and CO.
Explain how these pollutants are formed in internal combustion engines.
Explain why nonane has a higher boiling point than the structural isomer shown in part c).
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.
Write an overall equation for the reaction between ethane and bromine to form bromoethane and one other product.
Write an equation for the initiation step of this reaction.
The first equation in the propagation step is shown below.
C2H6 + Br• ➔ •C2H5 + HBr
Write an equation for the second propagation step.
Write a termination step for this reaction, resulting in the formation of butane.
Calculate the percentage by mass of bromine in the heaviest molecule containing two carbon atoms that could form when ethane reacts with a large excess of bromine. Give your answer to 3 significant figures.
This question is about the reactions of alkanes.
Alkanes can be used as fuels.
Write a balanced equation for the combustion of octane (C8H18) in excess oxygen.
Combustion of 45.6 g of octane produced 3.00 moles of CO2.
Show that this combustion was incomplete.
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.
Alkanes are saturated hydrocarbons which can be used as fuels.
Outline how fractions of hydrocarbons are obtained by the fractional distillation of crude oil.
Name and draw the skeletal formula of the alkane with the structural formula (CH3)2CHC(CH3)2CH2CH3.
Write an equation for the complete combustion of dodecane (C12H26).
Write an equation for the incomplete combustion of C11H24 to produce only H2O and a toxic gas.
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.
State the type of cracking that produces a high proportion of alkenes and give two conditions needed for the process.
The alkane with a molecular formula of C8H18 has several structural isomers. The structure of one of these isomers is shown below.
Draw the skeletal formula of the isomer shown in the diagram above.
Write an equation for the complete combustion of C8H18.
State under what conditions incomplete combustion of C8H18 would occur.
Write an equation for the incomplete combustion of C8H18 to produce CO as the only carbon-containing product.
Free radical substitution reactions can occur between alkanes and halogens in the presence of UV light.
Classify each of the following equations as initiation, propagation or termination by ticking the appropriate box in the table below.
Which of the following equations represents a propagation step in free radical substitution?
Which of the following species would not be formed in the free radical substitution of methane and bromine?
Chlorine reacts with alkanes.
Name the mechanism by which this reaction occurs.
Identify the initiation step of the reaction and its conditions.
Formulate equations for the two propagation steps and one termination step in the formation of chloromethane from methane.
This question is about halogenoalkanes.
Draw the structure of the alkene that would react with bromine to form 1,2-dibromo-3-methylpentane.
Name the halogenoalkane formed in the reaction between 2-methylbut-2-ene and bromine.
The halogenoalkane with the molecular formula C4H9Br has four structural isomers. Two of these isomers have been drawn below.
Draw and name the other two isomers.
Explain what is meant by the term displayed formula and draw the displayed formula of 2,3-dichloro-2-methylbutane.