7.1 Carbon compounds as fuels and feedstock

Question 1

What is crude oil? Where is crude oil found? How is crude oil formed?

Answer 1

• A mixture of molecules, mostly hydrocarbons.
• Found in rocks;
• Formed over millions of years from remains of ancient biomass (e.g. plankton buried in mud)

Question 2

What are hydrocarbons?

Answer 2

Molecules made up of hydrogen and carbon only (with different boiling point).

Question 3

What is the general formula of alkanes?

Answer 3

C_nH_2n+2

Question 4

What are alkanes?

Answer 4

A type of hydrocarbon which is saturated.

Question 5

Why are alkanes described as saturated?

Answer 5

The carbon atoms in alkanes are fully bonded to the hydrogen atoms.

Question 6

What are the first four alkanes?

Answer 6

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)
• Butane (C₄H₁₀)

Question 7

What are the properties of hydrocarbons needed to be known? (3)

Answer 7

• Viscosity
• Flammability
• Boiling point

Question 8

Describe the trends in the viscosity of hydrocarbons.

Answer 8

As the size of hydrocarbon molecules increase, they get more viscous.

Question 9

Describe the trends in flammability of hydrocarbons.

Answer 9

As the size of hydrocarbon molecules increase, the flammability decreases.

Question 10

Describe the trends in boiling points of hydrocarbons.

Answer 10

As the size of hydrocarbon molecules increases, the boiling point increases.

Question 11

Describe the process of combustion for hydrocarbons.

Answer 11

1. Hydrogen and carbon in hydrocarbon exothermically react with oxygen (oxidise) to produce:
   - (a) complete combustion: carbon dioxide and water.
   - (b) incomplete combustion: carbon or carbon monoxide and water.

Question 12

What is the word and unbalanced symbol equation for the combustion of hydrocarbons?

Answer 12

Alkane (C_nH_2n+2) + Oxygen (O₂) → Carbon dioxide (CO₂) + Water (H₂O)

Question 13

How do you balance a combustion equation (with an odd number of carbon atoms in the alkane)?

Answer 13

Start with carbon, then hydrogen, then oxygen.

Question 14

How do you balance a combustion equation (with an even number of carbon atoms in the alkane)?

Answer 14

1. Add a 2 to the alkane
2. Start balancing carbon atoms, then hydrogen, then oxygen.

Question 15

Describe the process of separating crude oil using fractional distillation. (5)

Answer 15

1. Crude oil boils as heated at 350ºC in furnace.
2. Hydrocarbons evaporate and turn into gas.
3. Crude oil vapour fed into fractionating column with a temperature gradient.
4. Hydrocarbons move up the column and condense when they reach their boiling point
5. The liquid fractions are then removed.

Question 16

What happens to very long and short chained hydrocarbons during fractional distilaltion?

Answer 16

• Long: very high boiling points, condense quickly, removed from bottom of column.
• Short: very low boiling points, don’t condense, removed from top of column as gases.

Question 17

What is a fraction?

Answer 17

Group of hydrocarbons with similar number of carbon atoms.

Question 18

What can the fractions of the crude oil be used for? (2)

Answer 18

• Fuel
• Feedstock for the petrochemical industry

Question 19

What are some useful fuels we depend on for modern lifestyle? (4)

Answer 19

• Petrol and diesel: cars and trucks
• Kerosene: jets
• Heavy duty oil: Ships
• Liquified petroleum gas: camping stoves

Question 20

What are useful materials made by the petrochemical industry, depended on for modern lifestyle? (4)

Answer 20

• Solvents
• Lubricants
• Detergents
• Polymers

Question 21

What bond do alkanes have?

Answer 21

Only single covalent bonds

Question 22

Why is cracking useful?

Answer 22

Some of the products of cracking can be usefully used a fuels as there is a high demand for fuels with small molecules.

Question 23

What is cracking?

Answer 23

A long-chain alkane is broken down (cracked) to produce smaller, more useful molecules.

Question 24

What is produced during cracking? (2)

Answer 24

An alkane and one or more alkenes

Question 25

What are some types of cracking? (2)

Answer 25

• Catalytic: 550ºC and [zeolite] catalyst
• Steam: 800ºC and no catalyst (steam)

Question 26

Why are alkenes useful molecules? (2)

Answer 26

• Used to make polymers.
• Used as starting material for other useful chemicals

Question 27

What is the test for alkenes? (3)

Answer 27

1) Add orange bromine water with solution.
2) Shake:
- (a) if solution is an alkene: bromine water turns colourless.
- (b) if solution is an alkane: bromine water stays orange

Question 28

What are the missing values:
C₂₅H₅₂ →C₂₀H₄₂ + C…H…

Answer 28

C₂₅H₅₂ →C₂₀H₄₂ + C₅H₁₀

Question 29

What are the missing values:
C₄₀H₈₂ → C…H… + C₇H₁₄

Answer 29

C₄₀H₈₂ → C₃₃H₆₈ + C₇H₁₄