C7 - organic chemistry

Question 1

what is a hydrocarbon?

Answer 1

any compound that is formed from carbon and hydrogen atoms only

Question 2

what is the general formula for alkanes?

Answer 2

CnH2n+2,

Question 3

what are alkanes?

Answer 3

a homologous series of saturated hydrocarbons

Question 4

what is a homologous series?

Answer 4

a group of organic compounds that react in a similar way

Question 5

what are the first four alkanes?

Answer 5

methane, ethane, propane, butane

Question 6

what is a displayed formula?

Answer 6

a drawing showing all the atoms and bonds in a molecule

Question 7

what is the formula for methane?

Answer 7

CH4

Question 8

what is the formula for Ethane?

Answer 8

C2H6

Question 9

what is the formula for propane?

Answer 9

C3H8

Question 10

what is the formula for Butane?

Answer 10

C4H10

Question 11

what are the properties of shorter hydrocarbons?

Answer 11

• less viscous
• more volatile (lower boiling points)
• more flammable

Question 12

what are the properties of longer hydrocarbons?

Answer 12

• more viscous
• less volatile (higher boiling points)
• less flammable

Question 13

what are short-chain hydrocarbons used for? why?

Answer 13

they are used as ‘bottled gases’ - stored under pressure as liquids in bottles - because of their low boiling points

Question 14

what is the equation for the complete combustion of a hydrocarbon?

Answer 14

hydrocarbon + oxygen -> carbon dioxide + water

Question 15

during the combustion of a hydrocarbon, what happens to the carbon and hydrogen?

Answer 15

they are both oxidised

Question 16

why are hydrocarbons used as fuels?

Answer 16

they release a lot of energy when they combust completely

Question 17

write a balanced symbol equation for the complete combustion of methane

Answer 17

CH4 + 2O2 -> CO2 + 2H20

Question 18

write a balanced symbol equation for the complete combustion of propane

Answer 18

C3H8 + 5O2 -> 3CO2 + 4H2O

Question 19

how is crude oil made?

Answer 19

from the remains of an ancient biomass, made up mainly of plankton, that’s been buried in mud for millions of years

Question 20

what type of fuel is crude oil?

Answer 20

a fossil fuel

Question 21

is crude oil renewable?

Answer 21

no

Question 22

what does crude oil consist of?

Answer 22

different lengths of hydrocarbons and a bit of sulfur

Question 23

what are the 4 steps to separating hydrocarbons by fractional distillation?

Answer 23

1. the oil is heated until most of it has turned into gas. The gasses enter a fractionating column, and everything that remains liquid is drained off
2. in the fractionating column there’s a temperature gradient (it’s hot at the bottom and cooler as you go up)
3. the longer hydrocarbons have high boiling points. They condense back into liquids early on, when they’re near the bottom. The shorter hydrocarbons have lower boiling points. They condense and drain out much later on, near to the top of the column where it’s cooler.
4. you end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points

Question 24

which fuels are obtained from the fractional distillation of crude oil, in order from the highest boiling point (collected at the bottom) to the lowest boiling point (collected at the top)

Answer 24

bitumen, heavy fuel oil, diesel oil, kerosene, petrol, LPG (liquefied petroleum gas)

Question 25

which two hydrocarbons does LPG mostly contain?

Answer 25

propane and butane

Question 26

what are the three oils that count as heavy fuel oil?

Answer 26

heating oil, fuel oil, lubricating oil

Question 27

what are the two main uses of crude oil?

Answer 27

1. oil provides the fuel for most modern transport. Diesel oil, kerosene, heavy fuel oil and LPG (liquid petroleum gas) all come from crude oil 2. the petrochemical industry uses some of the hydrocarbons from crude oil as a feedstock to make new compounds for use in things like polymers, solvents, lubricants and detergents

Question 28

what are organic compounds?

Answer 28

compounds containing carbon atoms

Question 29

what is cracking?

Answer 29

splitting up long-chain hydrocarbons

Question 30

why do we use cracking?

Answer 30

short-chain hydrocarbons are flammable so make good fuels and are in high demand. However, long-chain hydrocarbons form thick gloopy liquids like tar which aren't very useful, so we use cracking to turn a lot of the longer alkane molecules produced from fractional distillation into smaller, more useful ones.

Question 31

what are some of the products of cracking useful as?

Answer 31

fuels, e.g. petrol for cars and paraffin for jet fuel

Question 32

what does cracking produce other than alkanes?

Answer 32

alkenes

Question 33

which are more reactive: alkanes or alkenes?

Answer 33

alkenes

Question 34

what are alkenes used for?

Answer 34

they're used as a starting material when making lots of other compounds and can be used to make polymers

Question 35

what is the test for alkenes?

Answer 35

bromine water - when in the presence of an alkene it turns from bright orange to colourless

Question 36

what type of reaction is cracking?

Answer 36

a thermal decomposition reaction - it breaks molecules down by heating them

Question 37

what are the two methods of cracking?

Answer 37

1. catalytic cracking | 2. steam cracking

Question 38

what are the 3 steps to catalytic cracking?

Answer 38

1. you heat and vaporise long-chain hydrocarbons 2. then the vapour is passed over a hot powdered aluminium oxide catalyst 3. the long-chain molecules split apart on the surface of the specks of catalyst

Question 39

how do you perform steam cracking?

Answer 39

vaporise long-chain hydrocarbons, mix them with steam and then heat them to a very high temperature

Question 40

what is the word equation for cracking?

Answer 40

long-chain hydrocarbon molecule -> shorter alkane molecule + alkene

Question 41

how do you balance a chemical equation for cracking?

Answer 41

make sure that there is the same number of carbon molecules on both sides

Question 42

what is the general formula for alkenes?

Answer 42

CnH2n