Combined Chemistry - 5.7

Question 1

What two elements make up a hydrocarbon?

Answer 1

Hydrogen and Carbon

Question 2

What is crude oil a mixture of?

Answer 2

Hydrocarbons

Question 3

The ancient remains of plankton and other marine organisms is the origin of what finite resource?

Answer 3

Crude oil

Question 4

What is the general formula for a homologous series of alkanes?

Answer 4

C_nH_2n+2

Question 5

Draw the structure of and write the formula for the following alkanes:

a) Methane
b) Ethane
c) Propane
d) Butane

Answer 5

a) Methane, CH₄
b) Ethane, C₂H₆
c) Propane, C₃H₈
d) Butane, C₄H₁₀

Question 6

What process is used to separate the hydrocarbons found in crude oil?

Answer 6

Fractional Distillation

Question 7

Name three useful fuels obtained from crude oil.

Answer 7

Any three from:

• petrol
• diesel
• kerosene
• heavy fuel oil
• liquefied petroleum gas

Question 8

Name two useful materials that can be made from crude oil by the petrochemical industry.

Answer 8

Any two from:

• solvents
• lubricants
• polymers
• detergents.

Question 9

Explain how fractional distillation of crude oil works.

Answer 9

• Crude oil (a mixture of different length hydrocarbons) is heated.
• Different length fractions have different boiling points. When heated, the fractions evaporate and rise up the tower.
• The fractions cool down as they rise up the tower. When they reach their condensing point, they will condense, turn into a liquid and flow out of the tower.

Question 10

What is the relationship between the length of a hydrocarbon and…

a) …boiling point
b) …viscosity
c) …flammability

Answer 10

a) The longer the hydrocarbon, the higher the boiling point (or vice versa)
b) The longer the hydrocarbon, the higher the viscosity (or vice versa)
c) The longer the hydrocarbon, the lower the flammability (or vice versa)

Question 11

What type of reaction is shown by the equation below?

CH₄ + 2O₂ → CO₂ + 2H₂O

Answer 11

Combustion

Question 12

What are the products of complete combustion of a hydrocarbon?

Answer 12

carbon dioxide (CO₂) and water (H₂O)

Question 13

Write a balanced equation for the complete combustion of …

a) Propane
b) Ethane

Answer 13

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O

Question 14

Describe the conditions needed for:

a) Catalytic cracking
b) Steam cracking

Answer 14

a) Catalyst (Aluminium oxide) and high temperature
b) Steam and high temperature

Question 15

What are the products of cracking?

Answer 15

Alkanes and Alkenes

Question 16

What is the test for an alkene?

Answer 16

• Add bromine water
• Turns from orange to colourless

Question 17

Which are more reactive? Alkanes or Alkenes?

Answer 17

Alkenes

Question 18

a) Complete the equation below:

C₈H₁₈ → C₄H₁₀ + _______

b) What process is shown by the equation above?

* This is just an example, you will have to complete any equation for this process.

Answer 18

a) C₈H₁₈ → C₄H₁₀ + C₄H₈
b) Cracking

Question 19

Why is cracking useful for modern life?

Answer 19

• Alkenes (that are made from cracking) are used to make polymers
• Alkenes (that are made from cracking) are used as the starting material for the production of many chemicals
• Cracking produces short hydrocarbons that makes useful fuels