Higher: C7 - Organic chemistry

Question 1

What makes something “organic” in the chemical sense?

Answer 1

It contains carbon.

Question 2

What is crude oil?

Answer 2

• A finite resource found in rocks: the remains of an ancient biomass, consisting mainly of plankton that was buried in mud.
• Is a mixture of a large number of compounds, mostly hydrocarbons.

Question 3

What are hydrocarbons?

Answer 3

Molecules made only of hydrogen and carbon.

Question 4

Most of the hydrocarbons in crude oil are what?

Answer 4

Alkanes.

Question 5

What is the general formula for alkanes?

Answer 5

C_nH_{2n + 2}

Question 6

What is meant by the term “homologous series”?

Answer 6

A series of compounds with the same functional group and similar chemical properties.

Question 7

What are the names of the first four members of the alkanes?

Answer 7

• Methane
• Ethane
• Propane
• Butane

Question 8

What is fractional distillation and what is its purpose?

Answer 8

• The process by which hydrocarbons in crude oil are separated into fractions.
• The fractions can be processed to produce fuels and feedstock for the petrochemical industry.

Question 9

Explain how the process of fractional distillation works.

Answer 9

• Crude oil is heated until the hydrocarbons evaporate.
• The hydrocarbons rise through the column.
• The hydrocarbons condense and different fractions are extracted in different parts of the column.
• Longer hydrocarbons condense in the lower parts of the column; shorter ones in the upper parts.

Question 10

Name 5 fuels produced by fractional distillation from crude oil.

Answer 10

• Petrol
• Diesel oil
• Kerosene
• Heavy fuel oil
• Liquefied petroleum gases

Question 11

Name 4 useful materials produced by the petrochemical industry.

Answer 11

• Solvents
• Lubricants
• Polymers
• Detergents

Question 12

Why is there such a vast array of natural and synthetic carbon compounds?

Answer 12

Carbon atoms have the ability to form families of similar compounds (homologous series).

Question 13

What 3 properties of hydrocarbons depend on the size of molecules?

Answer 13

• volatility (boiling points)
• viscosity (runniness)
• flammability

Question 14

For hydrocarbons, how does boiling point change with increasing molecular size?

Answer 14

• Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome
• So their boiling points are higher
• Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules
• So they are more volatile

Question 15

For hydrocarbons, how does viscosity change with increasing molecular size?

Answer 15

• Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome
• So they are more viscous
• Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules
• So they are less viscous

Question 16

For hydrocarbons, how does flammability change with increasing molecular size?

Answer 16

• Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome
• So they are less flammable
• Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules
• So they are more flammable

Question 17

What happens during the combustion of hydrocarbons?

Answer 17

• The carbon and hydrogen in the fuels are oxidised
• Energy is released

Question 18

Write the general equation for the complete combustion of a hydrocarbon.

Answer 18

Hydrocarbon + oxygen → carbon dioxide + water

Question 19

What are alkenes?

Answer 19

Hydrocarbons with the functional group C=C (with a double carbon-carbon bond).

Question 20

What is cracking and what is its purpose?

Answer 20

• The process by which long-chain hydrocarbons are broken down to produce smaller, more useful molecules by thermal decomposition
• The products of cracking are alkanes and alkenes
• Some of the products of cracking - the small ones - are used for fuels because they are flammable

Question 21

How are alkenes (produced by cracking) useful?

Answer 21

• Used to produce polymers
• Used as starting materials for the production of many chemicals

Question 22

Name 2 types of cracking.

Answer 22

• Catalytic cracking
• Steam cracking

Question 23

Describe the conditions used for catalytic cracking.

Answer 23

• It is a thermal decomposition reaction
• Long-chain hydrocarbons are heated and vaporised
• Vapour is passed over a powdered aluminium oxide catalyst
• The molecules split apart on the surface of the specks of catalyst

Question 24

Describe the conditions used for steam cracking.

Answer 24

• It is a thermal decomposition reaction
• Long-chain hydrocarbons are heated and vaporised
• Vapour is mixed with steam and heated to a very high temperature
• The molecules split apart

Question 25

Which are more reactive: alkanes or alkenes?

Answer 25

Alkenes.

Question 26

How would you test for alkenes?

Answer 26

• Add bromine water, which is bright orange
• Positive result: solution goes colourless

Question 27

What is the general formula for alkenes?

Answer 27

C_nH_2n

Question 28

Which out of alkanes and alkenes are saturated and unsaturated? Explain why.

Answer 28

• Alkanes are saturated because all C-C bonds are single.
• Alkenes are unsaturated because they contain a double C-C bond (C=C).

Question 29

What are the names of the first four alkenes?

Answer 29

• Ethene
• Propene
• Butene
• Pentene

Question 30

How do alkenes combust?

Answer 30

• Alkenes can react completely with oxygen in the same way as all hydrocarbons.
• But they tend to react incompletely, burning with a smoky flame.