Carbon Compounds

Question 1

define crude oil and where it is found

Answer 1

a finite resource found in rocks

the remains of an ancient biomass consisting mainly of plankton that was buried in bud

Question 2

define a hydrocarbon

Answer 2

molecules made up of hydrogen and carbon only

Question 3

state the first four alkanes and their formulas

Answer 3

methane - CH4
ethane - C2H6
propane - C3H8
butane - C4H10

Question 4

state the general formula for alkanes

Answer 4

CnH2n+2

Question 5

name some of the fractions produced by crude oil

Answer 5

• petrol
• diesel oil
• kerosene
• heavy fuel oil
• liquefied petroleum gases

Question 6

explain the process of fractional distillation

Answer 6

• heated crude oil enters the bottom of the fractionating column, so vapour rise through the column: it is hotter at the bottom and cooler at the top
• the vaporised hydrocarbons with high boiling points condense towards the bottom of the column
• hydrocarbons with lower boiling points rise further up the column: different fractions condense at different heights due to different boiling points

long chain hydrocarbons have stronger intermolecular forces, so they have higher boiling points. this means they evaporate towards the bottom of the fractionating column as more energy is needed to break the forces of attraction between molecules and vice versa

Question 7

explain some properties of hydrocarbons

Answer 7

properties depend on the size of their molecules: boiling point, viscosity, and flammability

these properties influence how hydrocarbons are used as fuels

as we go up the fractionating column, the boiling point and viscosity decrease and the flammability increases

Question 8

fractions can be processed to produce fuels

give examples of some useful materials

Answer 8

solvents - nail varnish remover
lubricants - oil for car engines
polymers - polyethene
detergents - washing up liquid

Question 9

explain the combustion of hydrocarbons

Answer 9

releases energy
the carbon and hydrogen in fuels are oxidised and the complete combustion of a hydrocarbon produces carbon-dioxide and water

Question 10

how can hydrocarbons be broken down

Answer 10

they can be broken down (cracked) to produce smaller, more useful molecules

Question 11

describe the two methods on how cracking can take place

Answer 11

catalytic cracking - the hydrocarbon is heated t a high temperature and a catalyst is used

steam cracking - the hydrocarbon is heated and mixed with steam

Question 12

describe the test and result for an alkene

Answer 12

bromine water

orange/brown bromine water turns colourless if alkene is present