C7 - Organic Chemsitry

Question 1

What are hydrocarbons

Answer 1

Only contain hydrogen and carbon atoms

Question 2

What are Alkanes

Answer 2

Alkanes have all C-C single bonds 
Saturated compounds - each carbon atom forms 4 single covalent bonds 
They’re the simplest hydrocarbon. 
Have a general formula of CnH2n+2 
Alkanes are a homologous series

Question 3

What’s a homologous series

Answer 3

Group of organic compounds that react in a similar way

Question 4

Give example of Alkanes

Answer 4

Methane CH4
Ethane C2H8
Propane C3H8
Butane C4H8

Question 5

How do hydrocarbon properties change as chain gets longer

Answer 5

Shorter carbon chain - more runny hydrocarbons - less viscous
More volatile - lower boiling points and more flammable

Question 6

What is complete combustion

Answer 6

Plenty of oxygen - releases lots of energy
Hydrocarbon + oxygen -> carbon dioxide + water (+energy)
Both carbon and hydrocarbon oxidised

Question 7

Why are hydrocarbons used as fuels

Answer 7

Used as fuels as they release lots of energy

Question 8

What is fractional distillation used for

Answer 8

To separate hydrocarbon fractions

Question 9

Name the fractions of crude oil and their uses

Answer 9

Gas - cookers 
Petrol - car fuel 
Kerosene - airplane fuels 
Diesel oil - truck 
Heavy fuel oil - heating oil, lubricating oil 
Bitumen - layering roads

Question 10

What is crude oil

Answer 10

A mixture of hydrocarbons

Question 11

Describe process of fractional distillation of crude oil

Answer 11

Oil heated until most turns to gas
Gas enters fractionating column
Temperature gradient in column (hot at bottom, cool at top)
Longer hydrocarbons have higher boiling points
Condensed into liquids and drain out of column earlier on (near bottom)
Shorter hydrocarbons have lower boiling points - condensed towards top
You end up with crude oil mixture separated into different fractions

Question 12

What is the petrochemical industry

Answer 12

Use hydrocarbons from crude oil as feed stock to make new compounds for use in things like polymers, solvent, lubricants

Question 13

What are products from crude oil

Answer 13

All organic compounds (compounds with carbon atoms)

Range of products as carbon atoms can bond together to form homologous series - both Alkanes and Alkanes

Question 14

What is cracking

Answer 14

Splitting up long chain hydrocarbons

Question 15

Why is cracking used

Answer 15

Shirt chain - flammable - good fuel
Long chain - thick liquid which isn’t useful
So long chain turned into smaller ones so they’re useful as fuels

Question 16

What does cracking produce

Answer 16

Alkanes and Alkenes

Question 17

What are alkenes

Answer 17

More reactive - used as starting material when making other compounds that can be used to make polymers
Possess one or more double C-C bond
General formula of CnC2n

Question 18

How can bromine water test for alkenes

Answer 18

Bromine water into Alkanes - stay bright orange

Bromine water into alkene - colourless compound

Question 19

What are the different methods of cracking

Answer 19

Thermal decomposition reaction - breaking molecules down through heating
1. Heat long chain molecules to vaporise them
2. Vapour passed over hot powered Aluminium oxide catalyst
3. Long chain molecules split apart on surface of specks of catalyst - ‘catalyst cracking’
Steam cracking - heat and vaporise - mix with steam and heat to high temperature

Question 20

Properties of homologous series

Answer 20

Same general formula

Increasing chain length - higher boiling points

Question 21

First three alkenes formula

Answer 21

Ethene - C2H4
Propene- C3H6
Butene - C4H8