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 simplest type of hydrocarbon?

Answer 2

alkanes

Question 3

is the general form of an alkane

Answer 3

CnH2n+2

Question 4

alkanes are homologous series what does this mean?

Answer 4

a group of organic compounds that react in a similar way

Question 5

alkanes are saturated compounds, this means

Answer 5

each carbon atom forms four single covalent bonds

Question 6

what are the first four alkanes

Answer 6

methane
ethane
propane
butane

Question 7

the shorter the carbon chain……..

Answer 7

the less viscous the hydrocarbon is
the more volatile the hydrocarbon is
the more flammable the hydrocarbon is

Question 8

what are short chain hydrocarbons used for

Answer 8

bottles gasses, stored under pressure as liquids in bottles

Question 9

when does complete combustion occur?

Answer 9

when there plenty of oxygen

Question 10

what does complete combustion of hydrocarbon in oxygen release

Answer 10

lots of energy

Question 11

what are the waste products of complete combustion of hydrocarbons in oxygen?

Answer 11

carbon dioxide and water vapour

Question 12

what happens to carbon and hydrogen in combustion?

Answer 12

they are oxidised, they gain oxygen

Question 13

why are hrdocarbons used as fuels

Answer 13

they release a lot of energy when combust completely

Question 14

what is crude oil

Answer 14

a fossil fuel

Question 15

how is crude oil formed?

Answer 15

1) remains of plants and animals - mainly plankton, that died millions of years ago and were buried in mud.
2) over millions of years with high temp and pressure the remains turn to crude oil which can be drilled up from the rocks where its found.

Question 16

what are some examples of fossil fuels?

Answer 16

coal, oil and gas

Question 17

are fossil fuels non renewable?

Answer 17

YES they are finite resources and will one day run out

Question 18

what is fractional distillation used to separate?

Answer 18

hydrocarbon fractions

Question 19

what is crude oil a mixture of

Answer 19

lots of different hydrocarbons, most are alkanes

Question 20

how does fractional distillation work?

Answer 20

1) the oil is heated until most of it has turned to gas. the gasses enter a factional distillation column (and the liquid is drained off)
2) in the column there is a temperature gradient (hot at the bottom and cooler as you go up)
3) the longer hydrocarbons have high boiling points. they condense back into liquids and drain out of the column early on, when they re near the bottom. the short hydrocarbons have lower boiling points. they condense and drain out much later on, near the top of the column where its 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 21

crude oil uses:

Answer 21

fuel for most modern transport - cars, trains, planes.
diesel
kerosene
heavy fuel oil
liquid petroleum gas

petrochemical inductry use hydrocarbons from crude oil as a feedstock to make new compounds for thiungs like:
polymers
solvents
lubricants
detergents

Question 22

uses of crude oil:

Answer 22

Crude oil is an important source of:

fuels such as petrol, diesel, kerosene, heavy fuel oil and liquefied petroleum gases
feedstock for the petrochemical industry
A feedstock is a raw material used to provide reactants for an industrial reaction. A petrochemical is a substance made from crude oil using chemical reactions. For example, ethene is produced from crude oil. It is used as feedstock to make poly(ethene), a polymer.

Other useful substances made from compounds found in crude oil include:

solvents
lubricants
detergents

Question 23

why does crude oil produce a large variety of products?

Answer 23

carbon atoms can bond together to form different groups called homologous series. these groups contain similar compounds with many properties in common.

Question 24

what are short chain hydrocarbons used for?

Answer 24

they are flammable so they are used for fuels, they are in high demand

Question 25

what are long chain carbons used for

Answer 25

they form thick gloppy liquids like tar they are not very useful

Question 26

what happens to long chain hydrocarbons

Answer 26

they are spilt up by cracking

Question 27

as well as alkanes what is also produced in cracking?

Answer 27

alkenes

Question 28

what are alkenes?

Answer 28

hydrocarbons used a a starting material when making lots of other compounds and can be used to make polymers

Question 29

how do you test for alkenes?

Answer 29

1) when orange bromine water is added to an alkane, no reaction will happen and it will stay bright orange

2) if bromine water is added to an alkene a reaction occurs because alkenes are more reactive than alkanes. this results in a colourless compound being produced and the bromine water being decolorised.

Question 30

what are the products of cracking used for?

Answer 30

fuels eg petrol for cars and paraffin for jet fuel

Question 31

what type of reaction is cracking?

Answer 31

a thermal decomposition reaction - breaking molecules down by heating them

Question 32

how to do cracking?

Answer 32

1) heat long chain hydrocarbons to vaporise them
2) the vapour can be passed over a hot powdered aluminium oxide catalyst
3) the long chain molecules split apart on the surface of the specks of catalyst - this is catalytic cracking

Question 33

what is steam cracking:

Answer 33

vaporising the long chain hydrocarbon
mix it with steam
heat in very high temp