C9 - Hydrocarbons

Question 1

How is crude oil formed and where is it found

Answer 1

It is found in rocks
It is formed over millions of years when the remains of sea plants and animals than contained carbon dioxide got buried under rocks in high pressure and temperature conditions

Question 2

What is crude oil made of

Chemistry wise

Answer 2

• A mixture of compounds, mainly hydrocarbons

Question 3

What are the first four alkanes

Answer 3

Methane, Ethane, Propane and Butane

Question 4

What is a hydrocarbon

Answer 4

Molecules made up of hydrogen and carbon atoms only

Question 5

General formula for alkanes

Answer 5

CnH2n+2

Question 6

What are alkanes

Answer 6

A homologous series of saturated hydrocarbons where the bonds between all atoms are single covalent bonds. Each carbon atom bonds to 4 other atoms

Question 7

Properties of hydrocarbons and what they mean

Answer 7

• Viscosity - thickness of the fluid (how easily it flows)
• Flammability - how easily it combusts
• Volatility - the tendency to turn into a gas

Question 8

How does the size of a hydrocarbon relate to its properties

Answer 8

• Viscosity - as the size of the hydrocarbon increases, the viscosity increases - long chain hydrocarbons are extremely viscous
• Flammability - the shorter the hydrocarbon chain, the more flammable the hydrocarbon is and the cleaner (less smoky) the flame is
• Volatility - As the hydrocarbon chain size increases, the boiling point increases meaning the larger hydrocarbons are less volatile

Question 9

What happens when hydrocarbon fuels are combusted

Complete combustion

Answer 9

• They release energy to their surroundings (exothermic) when combusted
• The carbon and hydrogen atoms are oxidised to produce carbon dioxide and water (complete combustion)

Question 10

Equation for the complete combustion of a hydrocarbon e.g. methane

Answer 10

CH4 + 2O2 —> CO2 + 2H2O

Question 11

How is crude oil separated and what does this process form

Answer 11

• Through fractional distillation
• This process forms separate fractions which are groups of hydrocarbons with similar numbers of carbon atoms

Question 12

Stages of industrial fractional distillation

Answer 12

1. Crude oil is heated to a very high temperature so it evaporates
2. The crude oil vapour is then pumped into the bottom of the fractionating column which is hotter at the bottom and cooler at the top
3. The vapors rise up the column and condense when they reach their boiling points - this repeats for all remaining hydrocarbons
4. The liquid fractions are then removed

• The long chain hydrocarbons have high boiling points son they condense and are removed from the bottom
• The shorter chain ones habve low boiling points and some remain as gases and are collected from the top where the temperature is lower

Question 13

What does incomplete combustion produce

Answer 13

• Carbon monoxide
• This is a toxic, colourless and odourless gas

Question 14

Uses of common fractions of crude oil

Answer 14

• Petrol and diesel - fuels for cars
• Kerosene - jet fuel
• Liqified petroleum gases - camping stoves, gas cylinders
• Heavy fuel oil - ships
• Bitumen - roads

Question 15

How are fractions used in the petrochemical industry

Answer 15

They are uses as feedstock - this means they are used to create other chemicals
These new chemicals can include solvents, lubricants, detergents and polymers

Question 16

What is cracking and name the two types

Answer 16

The breaking down of a long chain hydrocarbon into a smaller, more useful and higher in demand hydrocarbons
It is a thermal decomposition reaction
The two types are catalytic cracking and steam cracking

Question 17

Conditions for catalytic cracking

Answer 17

• High temperature
• A catalyst e.g. aluminium oxide or porous pot

Question 18

Conditions needed for steam cracking

Answer 18

• High temperature
• Vaporised hydrocarbons are combined with steam

Question 19

Properties and use of alkanes

Answer 19

• Low reactivity
• Combust easily
• Therefore they are used as fuels

Question 20

Test for unsaturation

Answer 20

• Add bromine water
• If a molecule with a carbon-carbon double bond is used e.g. an alkene which is unsaturated, thte bromine water turns from orange to colourless because the alkene reacts with the bromine (forms 1,2 -dibromoethane)

Question 21

Properties that make a good fuel

Answer 21

• Flammable
• High volatility
• Low boiling point
• This is why shorter chain alkenes are very good fuels