Crude Oil (Edexcel IGCSE Science (Double Award): Chemistry)

This question is about hydrocarbons.

The table shows the formulae of some hydrocarbons.

i) Give the letters that represent hydrocarbons with the general formula C_nH_2n

(1)

ii) State why B is the only hydrocarbon shown as a displayed formula.

(1)

iii) Explain which two letters represent isomers.

(3)

iv) How many of the hydrocarbons are members of the homologous series of alkanes?

(1)

Many hydrocarbons are used as fuels. There are problems associated with this use.

i) Explain how the combustion of a hydrocarbon can lead to the formation of a poisonous gas.

(2) 

ii) State why this gas is poisonous to humans.

(1) 

Fuels used in cars often have sulfur compounds removed.

Explain how the combustion of these fuels in car engines still leads to the formation of acid rain.

Incomplete combustion occurs when there is insufficient oxygen for a reaction.

Which are the two main substances formed during incomplete combustion, aside from water?

The flow chart shows how ethene can be obtained industrially from crude oil.

Step 1 involves the use of a tall column. Describe how the diesel fraction is obtained from the crude oil in step 1.

In step 2, saturated compounds such as dodecane are obtained from the mixture of hydrocarbons in the diesel fraction. Explain why dodecane is described as a saturated hydrocarbon.

Which of these formulae is that of an alkane?

In step 3, cracking is used to convert alkanes into alkenes. Complete the equation to show the reaction in which one molecule of dodecane is converted into two molecules of ethene and one molecule of another hydrocarbon.

C₁₂H₂₆ → 2C₂H₄ + .....................................

Alkanes and alkenes both react with halogens, but in different ways. The equations for two examples of these different reactions are shown.

equation 1       C₂H₆+ Cl₂ → C₂H₅Cl + compound X

equation 2       C₂H₄ + Br₂ → C₂H₄Br₂

i) State the condition needed for the reaction in equation 1 to occur.

(1)

ii) Deduce the formula of compound X.

(1)

iii) Draw a dot-and-cross diagram to represent a molecule of C₂H₅Cl

Show only the outer electrons of each atom.

(2)

iv) Equation 2 shows an example of an addition reaction. State the type of reaction shown by equation 1.

(1)

Alkenes can be distinguished from alkanes using bromine water.

i) What colour change occurs in the reaction between propene and bromine water?

(1) 

ii) A compound formed in the reaction between propene and bromine water has the percentage composition by mass: 

C = 25.9%, H = 5.0%, Br = 57.6% and O = 11.5%

Calculate the empirical formula of this compound.

(3) 

Cars running on fossil fuels contribute a high amount of pollutants into the atmosphere, one of which is carbon dioxide. 

Which other gas is produced by the internal combustion engine in a car?

Propane is a hydrocarbon with the formula C₃H₈

State why propane is a hydrocarbon.

i) Name the poisonous gas that forms when propane is burned in a limited supply of air.

(1)

ii) State why this gas is poisonous to humans.

(1)

The diagram represents a molecule of propane.

Describe the forces of attraction between the atoms in a molecule of propane.

Propane can be produced by cracking. An equation for cracking is

C₁₃H₂₈ → C₃H₈ + 2C₃H₆ + 2C₂H₄

Explain why cracking is an important process in the oil industry.

Propane reacts with bromine in the presence of ultraviolet radiation.

i) Complete the equation for this reaction.

(2)

C₃H₈ + Br₂ → ............................... + ...............................

ii) Give the name of this type of reaction.

(1)

The diagram shows some processes involved in the oil industry. 

Which process represents cracking?

This question is about hydrocarbons.

State the meaning of the term hydrocarbon.

One homologous series of hydrocarbons is the alkanes. Pentane (C₅H₁₂) is an alkane.

i) When pentane burns completely in oxygen, carbon dioxide and water are produced. Give a chemical equation for this combustion reaction.

(2)

ii) Incomplete combustion can occur when the oxygen supply is limited. Give the names of two products of the incomplete combustion of pentane.

(2)

iii) One of the products of incomplete combustion is a poisonous gas. State why this gas is poisonous to humans.

(1)

iv) C₅H₁₂ has three isomers. The displayed formula for one of these isomers is

Draw the displayed formulae of the other two isomers.

(2)

Another homologous series of hydrocarbons is the alkenes. Alkenes are unsaturated hydrocarbons.

i) Give the general formula for the alkenes.

(1)

ii) State the meaning of the term unsaturated.

(1)

iii) Describe a test to show that a hydrocarbon is unsaturated.

(2)

Crude oil is a mixture of hydrocarbons.

Name the process used to separate crude oil into fractions.

Give one use of the kerosene fraction.

One of the hydrocarbons in the refinery gas fraction is an alkane with the structural formula CH₃CH₂CH₂CH_3.

i) Give the name of this alkane.

(1)

ii) Calculate the relative molecular mass (M_r) of this alkane.

(1)

One of the alkanes in the gasoline fraction has the displayed formula

i) Determine the molecular formula of this alkane.

(1)  

ii) Give the general formula for the alkanes.

(1)

Catalytic cracking is used to convert long‐chain alkanes into shorter‐chain alkanes.

i) Name the catalyst used in catalytic cracking.

(1)

ii) Explain why it is necessary to convert long‐chain alkanes into shorter‐chain alkanes.

(1)

Catalytic cracking also produces alkenes. C₁₁H₂₄ can undergo cracking to give pentane (C₅H₁₂) and two different alkenes. Complete the equation for this cracking reaction.

C₁₁H₂₄ → C₅H₁₂ + ............................+............................

Fractional distillation is the process by which crude oil is separated into simpler, more useful fractions.

Which of the following statements about the process of fractional distillation is correct?

Crude oil is an important source of organic compounds.

The diagram shows crude oil being separated into different fractions.

i) Name the process used to separate crude oil into different fractions.

(1)

ii) State what happens to the crude oil at X.

(1)

iii) Describe the differences between fraction B and fraction E. In your answer, refer to

• size of the molecules

• boiling point

• colour

• viscosity

(4)

Crude oil often contains sulfur as an impurity.

Explain why this is a problem when using crude oil fractions as fuels.

Kerosene, bitumen and diesel oil are fractions obtained through the fractional distillation of crude oil.

Which of the following shows the correct use of each fraction?

The diagram shows a fractionating column used to separate crude oil into fractions.

 i) Give a use for bitumen and a use for gasoline.

 (2)

 Use for bitumen: ....................................................................

 Use for gasoline: ...................................................................

  ii) Explain why bitumen is collected at the bottom of the fractionating column and gasoline is collected near the top of the fractionating column. 

(2)

There is a low demand for some of the fractions obtained from crude oil.   Cracking can be used to convert these fractions into more useful substances.

 i) State the conditions needed for cracking.

 (2)

 ii) Dodecane (C₁₂H₂₆) can be cracked to produce an alkane and two alkenes.

 Complete the equation by giving the formulae of the two alkenes.

 (2)

 C₁₂H₂₆ → C₇H₁₆ + ................................ + ....................................

This question is about octane (C₈H₁₈) which is produced in the gasoline fraction during fractional distillation of crude oil.

The diagram shows a fractionating column.

Describe how crude oil is separated into fractions in the fractionating column.

Octane can also be produced by the process of cracking. Give the conditions for cracking.