C7, Organic Chemistry

Question 1

what 2 elements do hydrocarbons contain

Answer 1

carbon and hydrogen atoms only

Question 2

general formula for alkenes

Answer 2

CnH2n+2

Question 3

displayed formula for butene

Answer 3

C4H10

Question 4

displayed formula for methane

Answer 4

CH4

Question 5

displayed formula for ethane

Answer 5

C2H6

Question 6

displayed formula for propane

Answer 6

C3H8

Question 7

waste products from complete combustion of hydrocarbons

Answer 7

• carbon dioxide

- water vapour

Question 8

how is crude oil formed

Answer 8

• from the remains of plants and animals (mainly plankton) that died millions of years ago and fell to the sea floor and were buried in mud.
• over millions of years under high temperatures and pressure the remains turned into crude oil
• drilled up from the ricks where it’s found

Question 9

where are the shortest carbon chains found in the fractional distillation column

Answer 9

have lower boiling points so condense and drain out much later on, near the top of the column where it’s cooler

Question 10

3 products made form crude oil

Answer 10

• petrol
• diesel oil
• kerosene (plane fuel)
• heavy fuel oil
• LPG (liquefied petroleum gas)

Question 11

why is cracking used

Answer 11

long-chained hydrocarbons form thick gloopy liquids (like tar) that aren’t useful so are often turned into smaller more useful ones through cracking

Question 12

what is cracking

Answer 12

• a thermal decomposition reaction, breaking molecules down by heating them

Question 13

steps used in cracking crude oil

Answer 13

1. heat long-chained hydrocarbons to vaporise them
2. vapour passed over a hot powdered aluminum oxide catalyst
3. the long-chain molecules split apart on the surface of the specks of catalyst

Question 14

how can fractional distillation be used to separate hydrocarbons fractions

Answer 14

1. oil heated until most of it has turned into gas
   - gasses enter a fractional column and liquid but are drained off
2. column is hot at the bottom and gets cooler as you go up
3. longer hydrocarbons have high boiling points - condense back into liquids and drain out of the column near the bottom. opposite for shorter hydrocarbons
4. end up with the crude oil mixture separated out into different fractions
   - each fraction separated out into different fractions
   - each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points