c9 - crude oil and fuels

Question 1

why is there a large number of carbon compounds?

Answer 1

carbon atoms have the ability to form families of similar compounds

Question 2

what can carbon atoms bond together to form?

Answer 2

chains and rings that form the ‘skeletons’ of molecules

Question 3

what are carbon compounds generally used for?

Answer 3

fuels to run cars, to warm homes, to generate electricity

Question 4

define crude oil

Answer 4

• a finite resource found in rocks
• mixture of many different compounds that boil at different temperatures
• is separated to make useful fuels

Question 5

how was crude oil formed?

Answer 5

formed over millions of years from plankton that were buried in mud

Question 6

give one way to separate a mixture of liquids?

Answer 6

distillation

Question 7

what are fractions?

Answer 7

a component of crude oil, which has its own particular molecular composition, weight, and boiling point

Question 8

define hydrocarbons

Answer 8

• molecules containing only hydrogen and carbon
• found in crude oil

Question 9

define alkanes

Answer 9

saturated hydrocarbons
- all their carbon-carbon bonds are single covalent bonds
- this means they contain as many hydrogen atoms as possible in each molecule and no more can be added

Question 10

give the general formula of alkanes

Answer 10

CₙH(2n+2)

Question 11

give the formula for methane

Answer 11

CH(4)

Question 12

give the formula for ethane

Answer 12

C(2)H(6)

Question 13

give the formula for propane

Answer 13

C(3)H(8)

Question 14

give the formula for butane

Answer 14

C(4)H(10)

Question 15

how is crude oil separated?

Answer 15

fractional distillation

Question 16

the larger the hydrocarbon molecule…

Answer 16

the higher the boiling point

Question 17

define process of fractional distillation

Answer 17

1) crude oil is vaporised and fed into a fractionating column (hot at bottom, cooler going up)
2) vapours move up column getting cooler
3) hydrocarbons condense to liquidwhen they reach level that is their boiling point
4) fractions are collected by outlets

Question 18

define viscosity

Answer 18

a measure of a fluid’s resistance to flow

Question 19

why do lighter fractions with lower viscosities make better fuels?

Answer 19

they ignite more easily and burn well, with cleaner frames

Question 20

what happens when pure hydrocarbons burn completely?

Answer 20

they are oxidised to carbon and water

Question 21

how can you test for water in complete combustion?

Answer 21

blue cobalt chloride paper turns pink in contact with water

Question 22

how can you test for carbon dioxide in complete combustion

Answer 22

limewater turns cloudy when carbon dioxide is present

Question 23

why can you see water produced when hydrocarbons in petrol and diesel burn on a winters day?

Answer 23

steam formed in combustion of fuel condenses when it cools down

Question 23

what happens when there is a limited supply of air when burning fuels?

Answer 23

• incomplete combustion
• carbon monoxide (CO) is produced

Question 24

what is cracking used for?

Answer 24

breaking large hydrocarbon molecules into smaller molecules

Question 25

define steam cracking

Answer 25

heating a mixture of hydrocarbon vapours and steam to a very high temperature

Question 26

define catalytic cracking

Answer 26

passing hydrocarbon vapours over a hot catalyst

Question 27

define thermal decomposition

Answer 27

breakdown of a compound through heating

Question 28

what happens during cracking?

Answer 28

thermal decomposition reactions produce a mixture of smaller molecules including alkanes

Question 29

why are alkanes more useful as a fuel?

Answer 29

they have smaller molecules

Question 30

why would an oil company want to crack larger hydrocarbons to make smaller alkanes?

Answer 30

improves supply of fuels

Question 31

define alkenes

Answer 31

unsaturated hydrocarbons - contain fewer hydrogen atoms than alkanes with the same number of carbon atoms - have a double covalent carbon bond in molecules

Question 32

give general formula of alkenes

Answer 32

C(n)H(2n)

Question 33

how are alkanes formed?

Answer 33

formed in cracking

Question 34

give a use of alkenes?

Answer 34

used to produce polymers and solvents

Question 35

why are alkEnes more reactive than alkAnes?

Answer 35

alkenes have a double bond between two carbon atoms

Question 36

how can you test for unsaturated compounds?

Answer 36

alkenes present if bromine water turns from orange to colourless