C7 - Organic Chemistry

Question 1

What is a hydrocarbon?

Answer 1

• A compound that is formed from carbon and hydrogen atoms only

Question 2

What are alkanes?

Answer 2

• The simplest type of hydrogencarbons (saturated hydrocarbons)
• A homologous series (a group of organic compounds that react in a similar way)

Question 3

What is the general formula for alkanes?

Answer 3

C (n) H (2n +2)

Question 4

What are the first four alkanes?

Answer 4

• Methane
• Ethane
• Propane
• Butane

Question 5

What happens to the viscosity as the length of a hydrocarbon increases?

Answer 5

• Increases as well (becomes more gloopy)

Question 6

What happens to the volatility of hydrocarbons as the length increases?

Answer 6

• They become less volatile, and have higher boiling points

Question 7

What happens to the flammability of a hydrocarbon as the length increases?

Answer 7

• It makes it harder to ignite

Question 8

What is the complete combustion of hydrocarbons?

Answer 8

hydrogen + oxygen -> carbon dioxide + water

Question 9

What happens during combustion?

Answer 9

• Both carbon and hydrogen from the hydrocarbons are oxidised

Question 10

What are hydrocarbons used for?

Answer 10

• Fuels due to the amount of energy they release when they combust completely

Question 11

What is crude oil and how is it formed?

Answer 11

• Fossil fuel
• It is formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were burried in mud
• Over millions of years, with high temperature and pressure, the remains turn to crude oil, which can be drilled up from the rocks where it’s found

Question 12

What are non-renewable fuels?

Answer 12

• Coal, oil and gas are called non-renewable fuels as they take so long to make that they’re beings used up much faster than they’re being formed (finite resources) so one day they will run out

Question 13

What is the process of separating crude oil into it’s different compounds (as crude oil is a mixture)?

Answer 13

Fractional distillation

Question 14

How does fractional distillation work?

Answer 14

• The oil is heated until most of it has turned into gas (they enter a fractionating column)
• In the column there’s a temperature gradient (it’s hot at the bottom and cooler as you go up)
• The longer hydrocarbons have high boiling points, so they condense back into liquids and drain out of the column early on, when they’re near the bottom. Similarly it’s the opposite but the same concept for the shorter hydrocarbons

Question 15

What is at the top of the FD chain?

Answer 15

LPG (liquified petroleum gas)

Question 16

What is the 2nd compound in FD?

Answer 16

Petrol for cars

Question 17

What is the 3rd compound in FD?

Answer 17

Kerosene fuel for planes

Question 18

What is the 4th compound in FD?

Answer 18

Diesel for cars

Question 19

What is the 5th compound in FD?

Answer 19

Heavy fuel oil for heating, fuel or lubricating

Question 20

Why is crude oil important?

Answer 20

• Provides the fuel for most modern transport
• The petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents

Question 21

Why are short-chain hydrocarbns in high demand?

Answer 21

• The flammability make good fuels

Question 22

What is cracking

Answer 22

The process that breaks down long-chain hydrocarbons into shorter-chain molecules that are more useful (thermal decomposition)

Question 23

Why is cracking useful?

Answer 23

• Long hydrocarbons form thick gloopy substances like tar, so they can be broken down into smaller chains of hydrocarbons

Question 24

What can cracking produce?

Answer 24

• Alkenes which are a lot more reactive than alkanes

- They are often used as a starting material when making lots of other compounds and can be used to make polymers

Question 25

What can be used to test for alkenes?

Answer 25

Bromine water

Question 26

What are the colour tests for Bromine water and alkenes?

Answer 26

• When orange bromine water is added to an alkane, no reaction will happen and it’ll stay bright orange
• If it’s added to an alkene, the bromine reacts with the alkene to make a colourless compound - so that bromine water is decolourised

Question 27

What is cracking?

Answer 27

Thermal decomposition reaction, where you break down molecules by heating them

Question 28

What are the steps to cracking?

Answer 28

• Heat long-chain hydrocarbons to vaporise them
• Pour the vapour over a hot powdered aluminium oxide catalyst
• The long-cain molecules split apart on the surface of the specks of catalyst (catalytic catalyst)
• You can also crack hydrocarbons if you vapourise them, mix them with steam and then heat them to a very high temperature (steam cracking)