Alkanes - questions and answers

1) Some of the hydrocarbons in kerosene have the formula C10H22. What is the name of the straight chain hydrocarbon with the formula C10H22?

ii) draw the skeletal formula of one branched chain isomer with the formula C10H22.

iii) Explain why the straight chain isomer of C10H22 has a higher boiling point than any of its branched chain structural isomers.

iv) Explain why the straight chain isomer of C10H22 is converted by the petroleum industry into its branched chain isomers.

2) Reaction mechanism shows the individual steps that take place during a reaction. Methane reacts with bromine in the presence of ultraviolet radiation to form several products. Two of these products are bromomethane and hydrogen bromide. Write an equation for the reaction between methane and bromine to make bromomethane and hydrogen bromide.

ii) Name one other bromine-containing organic product which is formed when methane reacts with bromine.

iii) The mechanism for this reaction is called radical substitution.
Describe the mechanism for the radical substitution of methane by bromine to make bromomethane.
Use the mechanism to suggest why a small amount of ethane is also formed.
In your answer, you should organise your answer and use the correct technical terms.

3) Crude oil is a source of hydrocarbons which can be used as fuels or for processing into petrochemicals. Octane, C8H18, is one of the alkanes present in petrol. Carbon dioxide is formed during the complete combustion of octane.
C8H18 + 12½O2 → 8CO2 + 9H2O
What is the general formula for an alkane?

4) Oil companies process hydrocarbons, such as octane, into branched and cyclic hydrocarbons that promote efficient combustion in petrol.
Draw the skeletal formulae of a branched hydrocarbon and a cyclic hydrocarbon, each containing eight carbon atoms.

5) Butane, C4H10, reacts with chlorine to produce a chloroalkane with molecular formula C4H9Cl.
The reaction is initiated by the formation of chlorine radicals from chlorine.
What is meant by the term radical?

ii) State the conditions necessary to bring about the formation of the chlorine free radicals from Cl2.

iii) State the type of bond fission involved in the formation of the chlorine radicals.

iv) The chlorine radicals react with butane in several steps to produce C4H9Cl.
Write equations for the two propagation steps.

6) Butane, C4H10, under certain conditions, reacts with Cl2 to form a mixture of chlorinated products. One possible product is C4H9Cl.
C4H10 + Cl2 -> C4H9Cl + HCl
ai) State the conditions.

ii) Write equations to show the mechanism of this reaction.
initiation: ................................................................
propagation:
.................................................................
.................................................................

iii) Write one equation for a reaction that would terminate this mechanism.

iv) State the type of bond fission involved in the initiation step

ii) Draw the skeletal formula of compound J.

iii) In addition to compound J, suggest one other possible structural isomer of C4H8Cl2 that could have been formed in this reaction.

7) Hexane reacts with Br2 in the presence of ultraviolet light.
C6H14 + Br2 -> C6H13Br + HBr
i) State the type of reaction.

ii) Identify the three possible structural isomers of the product, C6H13Br, that could be formed from this reaction with hexane.

8) Alkanes can be separated from crude oil because they have different boiling points.
Explain the variation in boiling points of alkanes.

9) Isomer L, C5H10, reacts with Cl2 in the presence of UV light to produce the organic product C5HgCl. The reaction takes place in three stages: initiation, propagation and termination.
i) The reaction is initiated by the fission of Cl2. State the type of fission involved.

ii) Write an equation to illustrate the fission of Cl2 in (i).

iii) The fission of Cl2 leads to a chain reaction involving two propagation steps. Complete the equations for the two propagation steps.

C5H10 + ......... -> ∙C5H9 + .........

∙C5H9 + ......... -> ........... + ..........