Alkanes

Question 1

What is an alkane

Answer 1

Saturated hydrocarbon found in crude oil

Question 2

Steps for fractional distillation

Answer 2

The vaporised oil enters the column and rises through the trays
The column has a temperature gradient where it is cooler at the top
As vapour rises the longest hydrocarbons run down the the bottom and don’t vaporise
The shortest hydrocarbons come off as a gas at the top of the column
Fractions are removed and collected at different levels

Question 3

5 fractions of crude oil and their uses

Answer 3

Gas - used in stove gas
Kerosine - used as jet fuel and heating
Diesel oil - used as diesel fuel
Fuel oil - used in ships and power stations
Petrol - used in petrol cars

Question 4

Gas fraction of crude oil?

Answer 4

Naptha

Question 5

Why is cracking necessary

Answer 5

Heavier fractions are in lower demand than lighter fractions which are more valuable

Question 6

2 types of cracking

Answer 6

Thermal
Catalytic

Question 7

Thermal cracking conditions and products

Answer 7

1000°C
70atm pressure

Mainly alkenes

Question 8

Catalytic cracking conditions and products

Answer 8

450°C and slight pressure with zeolite catalyst
Mainly aromatic hydrocarbons

Question 9

Why is zeolite useful in catalytic cracking

Answer 9

Lowers temperature and pressure needed for cracking to occur, lowering costs and speeding up the process

Question 10

Why are alkanes good fuels

Answer 10

Most burn readily to release large amounts of energy

Question 11

Alkane complete combustion products

Answer 11

CO2 and water

Question 12

Alkane incomplete combustion products

Answer 12

Carbon monoxide and carbon and water (sometimes CO2 aswell)

Question 13

Problems with soot and carbon monoxide (+ how to remove CO2)

Answer 13

Soot can cause breathing problems and clog up engines
CO is poisonous and bonds to haemoglobin preventing oxygen binding - can be removed using a catalytic converter

Question 14

What is the greenhouse effect

Answer 14

CO2 bonds absorb infrared radiation from the sun but emit some of it back into the earth

Question 15

What is the ozone layer

Answer 15

Lowest level of atmosphere made of sunlight, hydrocarbons and nitrogen dioxide

Question 16

How is photochemical smog made?

Answer 16

Solid carbon particulates mixed with ozone

Question 17

What do photochemical smog and ozone do to humans?

Answer 17

Photochemical smog harms the respiratory system in animals and damaged plants
Ozone is also toxic to humans too

Question 18

How is nitrogen oxide made

Answer 18

When nitrogen and oxygen from the air combine under high temps and pressure in car engines

Question 19

How do catalytic converters help the environment

Answer 19

Reduce the amount of unburnt hydrocarbons and nitrogen oxides going into the atmosphere

Question 20

Acid rain problems

Answer 20

Damages plants, kills fish and causes erosion of buildings

Question 21

How does burning fossil fuels cause acid rain

Answer 21

Some fossil fuels contain sulfur based impurities
When burned the sulfur reacts with oxygen to produce sulfur dioxide
Sulfur dioxide is an acidic gas which reacts with water in the atmosphere to form sulfuric acid in acid rain (nitrogen oxides do this too)

Question 22

How to remove SO2 from flue gases

Answer 22

Wet scrubbing
Calcium carbonate or oxide is dissolved in water and acidic sulfur dioxide gas is sprayed on

Question 23

Free radical substitution (alkanes to halogenoalkanes) CH4 + Cl2 -> CH3Cl + HCL

Answer 23

UV light condition
Initiation: sunlight breaks the Cl-Cl bond in a process called photodissociation Cl-Cl -> 2Cl•
Propagation: Cl• + CH4 -> HCL + •CH3
•CH3 + Cl2 -> CH3Cl + •Cl
Termination: •CH3 + •Cl -> CH3Cl
(2•Cl -> Cl2 and 2•CH3 -> CH3CH3)