Topic 7: Organic Chemistry

Question 1

What is a hydrocarbon?

Answer 1

A molecule made up of only carbon and hydrogen atoms

Question 2

How is crude oil formed? (6)

Answer 2

1) Microscopic plants obtain energy from photosynthesis
2) Plankton and tiny animals eat the plants
3) Plants and animals die
4) They become buried in sediment unable to decay
5) Layers of sediment increase pressure
6) Over millions of years chemical reactions turn the remains into oil

Question 3

Where is crude oil found?

Answer 3

Oil rises through permeable sedimentary rock until it reaches an impermeable layer where it is then drilled for

Question 4

What makes up crude oil?

Answer 4

A mixture of hydrocarbons of different lengths

Question 5

What are the properties of heavy fractions or long-chain hydrocarbons? (4)

Answer 5

1) High boiling points
2) High viscosity
3) Low volatility (or how quickly it evaporates)
4) Low flammability

Question 6

What are the properties of light fractions or small-chain hydrocarbons? (4)

Answer 6

1) Low boiling points
2) Low viscosity
3) High volatility (or how quickly it evaporates)
4) High flammability

Question 7

What are the most common hydrocarbons?

Answer 7

Alkanes

Question 8

What are alkanes? (3)

Answer 8

1) The simplest hydrocarbons
2) Saturated hydrocarbons where carbon atoms form four single covalent bonds
3) A homologous series

Question 9

What are saturated hydrocarbons?

Answer 9

Hydrocarbons which only contain single covalent bonds

Question 10

What is a homologous series?

Answer 10

A group of organic (contains carbon) compounds that react in a similar way

Question 11

Name the first ten alkanes

Answer 11

Methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane and decane

Question 12

Why do alkanes make good fuels? (2)

Answer 12

1) They are fairly unreactive but are flammable

2) When completely combusted they release a lot of energy

Question 13

What is the general formula of an alkane?

Answer 13

CnH2n+2

Question 14

What forms when hydrocarbons are completely combusted in a plentiful oxygen supply? (2)

Answer 14

1) hydrocarbon + oxygen –> carbon dioxide + water

2) hydrocarbon + oxygen –> lots of energy

Question 15

What forms when hydrocarbons are completely combusted in a poor oxygen supply?

Answer 15

Carbon monoxide

Question 16

What are the properties of carbon monoxide?

Answer 16

1) Colourless
2) Odorless
3) Toxic

Question 17

How is carbon monoxide dangerous?

Answer 17

Carbon monoxide takes oxygen out of the haemoglobin in the blood to become carbon dioxide which means cells do not get enough oxygen

Question 18

What does breathing carbon monoxide cause? (4)

Answer 18

1) Breathing difficulties
2) Headaches
3) Unconsciousness
4) Death

Question 19

What is fractional distillation? (2)

Answer 19

1) The process of separating crude oil into groups of hydrocarbons with similar numbers of carbon atoms
2) The separation of a liquid mixture into fractions differing in boiling point

Question 20

What are the three stages of fractional distillation?

Answer 20

1) Evaporation
2) Condensation
3) Collection

Question 21

Describe the process of fractional distillation (5)

Answer 21

1) Crude oil is heated until evaporation
2) Crude oil vapour is put into the bottom of a fractionating column
3) The column has a temperature gradient (bottom is hot while top is cool)
4) As the vapour rises, longer hydrocarbons with high boiling points will condense and drain out near the bottom
5) As the vapour rises, shorter hydrocarbons with low boiling points will condense and drain out near the top

Question 22

Give examples of the end products of fractional distillation (2)

Answer 22

1) Fuel for most modern transport

2) Feedstock for polymers, solvents, lubricants and detergents

Question 23

What is cracking?

Answer 23

The process where long-chain hydrocarbons are broken down into shorter, more useful molecules

Question 24

What are the two ways of cracking? (2)

Answer 24

1) Catalytic cracking

2) Steam cracking

Question 25

How does steam cracking work?

Answer 25

Vaporised long-chain hydrocarbons are mixed with steam and then heated to extreme temperatures

Question 26

How does catalytic cracking work? (4)

Answer 26

1) Long-chain hydrocarbons are vaporised
2) Vapour is passed over a hot powdered aluminium oxide catalyst
3) Long-chain hydrocarbons are split apart on the surface of the catalyst
4) Short-chain alkanes and alkenes are formed

Question 27

What are alkenes used for? (2)

Answer 27

1) Starting materials for many chemicals

2) Being combined to make polymers