C7 - Organic Chemistry

Question 1

What are hydrocarbons

Answer 1

Any compound made from carbon and hydrogen only

Question 2

Name the first four alkanes

Answer 2

methane
ethane
propane
butane

Question 3

Define a homologous series

Answer 3

A group of organic compounds that have similar chemical properties, due to them having the same functional group.

Question 4

What is the general formula for alkanes

Answer 4

Cn H2n+2

Question 5

Describe the trend as the size of alkanes increases (6 marks)

Answer 5

Boiling point/melting point increases
Shorter alkanes are more volatile evaporate more easily - because of low boiling point
Longer alkanes are more viscous
Shorter alkanes are more flammable

Question 6

Describe the equation for complete combustion

Answer 6

hydrocarbon + oxygen → carbon dioxide + water

Question 7

Write a balanced equation for the complete combustion of propane

Answer 7

C3H8 + 5O2 → 3C02 + 4H2O

Question 8

Is combustion endothermic or exothermic

Answer 8

exothermic

Question 9

Incase you get a odd number of oxygen while balancing your equation what should you do

Answer 9

Double everything to remove the decimal

Question 10

What is crude oil/how was it made

Answer 10

A finite resource (fossil fuel) formed from remains of plants and animals, mainly plankton that died millions of years ago and were buried in mud

Question 11

Why are fossil fuels like coal, oil and gas called non-renewable fuels

Answer 11

They take so long to make that they are being used up faster than being formed

Question 12

Describe how hydrocarbons in crude oil is separated using fractional distillation works (6 marks)

Answer 12

Crude oil is a mixture of hydrocarbons with different boiling points
Oil is heated until most of it has turned gas
Gas enters a fractionating column
Column has a temperature gradient (Hot at the bottom cooler as you go up)
Longer hydrocarbons have high boiling points - condense back into liquids and drain out of the column early on when they’re near the bottom where it is hotter
Shorter hydrocarbons have lower boiling points - condense and drain out much later on, near the top where it is cooler

Question 13

What is feedstock

Answer 13

A feedstock is a raw material used to provide reactants for an industrial reaction.

Question 14

What is a petrochemical

Answer 14

A petrochemical is a substance made from crude oil, via chemical reactions.

Question 15

What two things does cracking produce

Answer 15

alkanes and alkenes

Question 16

What is the test for alkanes/alkenes and how is it used

Answer 16

Bromine water - orange bromine water added to an alkane - no reaction - stays bright orange
Orange bromine water added to an alkene - turns into a colourless solution

Question 17

What is cracking

Answer 17

Thermal decomposition reaction that breaks molecules down by heating them

Question 18

Describe the steps for catalytic cracking (3 marks)

Answer 18

Heat long-chain hydrocarbons to vaporize them
Vapour is passed over a hot powdered aluminium oxide catalyst
This breaks the long chain alkanes into a shorter chain alkane and an alkene

Question 19

Describe the steps for steam cracking (2 marks)

Answer 19

Vaporize - mix with steam then heat them to a very high temperature