Alkanes (Edexcel IGCSE Chemistry)

The table shows the molecular formulae of six organic compounds, A, B, C, D, E and F.

i) Explain which homologous series compound B belongs to. 

(2)

 ii) Give the letter of the compound that has the same empirical formula as its molecular formula. 

(1)

 iii) Compound F exists as two isomers.

 Explain what is meant by the term isomers.

 Include the structures of the two isomers of compound F in your answer. 

(3)

Describe how compound D can be obtained from crude oil using the industrial process of fractional distillation.

Compound C can be used to make a polymer.

 i) State the type of polymer formed from compound C. 

(1) 

ii) Name the polymer formed from compound C.

 (1)

 iii) Draw the structure of this polymer.

 Include the displayed formula of the repeat unit.

 (2)

This question is about alkanes and alkenes.

i) Complete the boxes by giving the missing information about the alkane with the molecular formula C₂H₆ 

(3)

ii) Complete the chemical equation for the complete combustion of the alkane C₂H₆ 

(1)

...........C₂H₆ + ...........O₂ → ...........CO₂ + ...........H₂O

 iii) Incomplete combustion occurs when the air supply is limited.

 Give the names of two products of incomplete combustion. 

(2)

An alkene with molecular formula C₄H₈ reacts with bromine to form a compound with molecular formula C₄H₈Br₂

 i) What is the name of this type of reaction? 

(1)

 ii) Draw displayed formulae for two different alkenes with the molecular formula C₄H₈ 

 (2)

 iii) State the term used for compounds with the same molecular formula but different structural formulae. 

(1)

The alkene C₃H₆ can be polymerised to form the polymer poly(propene).

 i) Complete the equation for this polymerisation reaction.

(2)

 ii) Two ways of disposing of polymers such as poly(propene) are:

• burying them in landfill sites

• burning them to release heat energy

Discuss the environmental problems caused by these two methods of disposal.

(3)

Ethane and bromine can react in the following reaction: 

What name is given to this type of reaction?

Methane and bromine react to form bromomethane and hydrogen bromide. 

What does this reaction occur in the presence of? 

Alkanes are hydrocarbons. The structure of a molecule of butane is shown.

Which of the following is the empirical formula for butane?

The graph below shows the boiling points of some alkanes plotted against the number of carbon atoms in one molecule of each alkane.

A molecule of pentane contains five carbon atoms. Use the graph to estimate the boiling point of pentane.

boiling point of pentane = .............................................................. °C

When pentane reacts with bromine in the presence of ultraviolet radiation, bromopentane is produced.

i) State the name of the other product formed in this reaction.

(1)

ii) Give the molecular formula of bromopentane.

(1)

Draw the displayed formula of the three isomers of bromopentane.

There are three isomers with the molecular formula C₅H₁₂ 

One of these isomers is pentane. 

The displayed formula for pentane is

 i) State what is meant by the term isomers. 

(2) 

ii) Draw the displayed formula for another isomer of C₅H₁₂ 

 (2)

Pentane reacts with bromine in the presence of ultraviolet radiation.

 i) Complete the equation for this reaction.

 (2) 

C₅H₁₂ + Br₂ → .................... + ....................

 ii) Give the name of this type of reaction.

 (1)

The alkanes are generally unreactive. Their reactions include combustion and substitution.

The complete combustion of an alkane gives carbon dioxide and water.

 i) 10 cm³ of butane is mixed with 100 cm³ of oxygen, which is an excess. The mixture is ignited. What is the volume of unreacted oxygen left and what is the volume of carbon dioxide formed?

 C₄H₁₀ (g) + 6.5O₂ (g) → 4CO₂ (g) + 5H₂O (l)

 Volume of oxygen left = .................................................. cm³

 Volume of carbon dioxide formed = .................................................. cm³

 (2)

 ii) Why is the incomplete combustion of any alkane dangerous, particularly in an enclosed space?

 (2)

Many organic compounds which contain a halogen have chloro, bromo or iodo in their name.

The following diagram shows the structure of 1-chloropropane. 

i) Draw the structure of an isomer of this compound.

(1)

ii) Describe how 1-chloropropane could be made from propane.

(2)

iii) Suggest an explanation why the method you have described in (ii) does not produce a pure sample of 1-chloropropane.

(2)

Organic halides react with water to form an alcohol and a halide ion.

CH₃–CH₂–I + H₂O → CH₃–CH₂–OH + I^–

i) Describe how you could show that the reaction mixture contained an iodide ion.

(2)

ii) Name the alcohol formed when 1-chloropropane reacts with water.

(1)

An alkane containing six carbon atoms can exist as a number of different structures. Two of these structures are shown below.

Compare the structures of hexane and cyclohexane.

A sample of one of these structures was found to contain 83.72% carbon. 

i) Calculate its empirical formula.

Show your working.

(3)

ii) Deduce whether the sample was hexane or cyclohexane.

(1)

i) Give the molecular formula of cyclohexane.

(1)

ii) Draw the displayed formula of an isomer of cyclohexane.

(1)

In the presence of ultraviolet radiation, hexane will react with chlorine to form hydrogen chloride and another compound, X. Compound X will undergo a further substitution reaction when heated with sodium hydroxide solution to form sodium chloride and a compound with the formula CH₃(CH₂)₅OH.

Cyclohexane will also react with chlorine in the presence of ultraviolet to form hydrogen chloride and compound Y. When heated with sodium hydroxide solution, compound Y will undergo a further substitution reaction to form sodium chloride and another product, Z. Give the names of compounds X, Y and Z. 

Three consecutive straight-chain members of the same homologous series are pentane, hexane and heptane.

Pentane is the compound containing the least number of carbon atoms.

Suggest the molecular formula of heptane.

Draw one line from each alkane to its boiling point.

Alkynes are hydrocarbons with the general formula C_nH_2n-2. The alkyne containing 2 carbon atoms is ethyne, C₂H₂. 

State, with a reason, whether the boiling point of ethyne would be expected to be higher or lower than the boiling point of ethane, C₂H₆.

Complete the dot-and-cross diagram for a molecule of ethyne, C₂H₂.

This question is about the reactions of the gas ethane, C₂H₆.

Write the equation which represents the complete combustion of 1 mole of ethane.

Ethane will react with chlorine in the presence of ultraviolet radiation to form chloroethane and hydrogen chloride.

C₂H₆ (g) + Cl₂ (g) → C₂H₅Cl (g) + HCl (g)

Rewrite this equation to show the displayed formulae of the reactants and products.

The enthalpy change of this reaction is -122 kJ/mol.

Use the bond energy data in the table below to calculate the bond energy of the C-Cl bond.

bond energy ........................................................ kJ / mol

Use your answer from part c) to suggest which compound, ethane or chloroethane, is the more reactive. Explain your answer.