C7

Question 1

what elements do hydrocarbons contain?

Answer 1

hydrogen and carbon

Question 2

what are alkanes and what are some things about them?

Answer 2

alkanes are the simplest form of hydrocarbons

• they’re saturated compounds (each carbon atom forms four covalent bonds)
• alkanes are a a homologous series (a group of organic chemicals that act in the same way)

Question 3

what are the first four alkanes? what are their symbols?

Answer 3

methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10)

Question 4

what are hydrocarbons?

Answer 4

the simplest organic compound

Question 5

what occurs when a hydrocarbon chain gets longer

Answer 5

its properties changes

Question 6

describe what happens when a hydrocarbon chain gets shorter

Answer 6

its hydrocarbon gets runnier, it becomes more volatile (lower boiling points) and it becomes more flammable.

Question 7

when does complete combustion occur?

Answer 7

when theres plenty/enough of oxygen

Question 8

what is released by combustion of any hydrocarbon?

Answer 8

lots of energy with waste products of carbon dioxide and water vapour.

Question 9

what is the word equation for combustion?

Answer 9

hydrocarbon+oxygen——–>carbon dioxide+water

Question 10

why are hydrocarbons used as fuels?

Answer 10

because they can be separated into different compounds and are a good source of heat

Question 11

crude oil can be used for fuel. what has to be done before?

Answer 11

the different hydrocarbons have to be separated through fractional distillation.

Question 12

what is crude oil and how is it formed?

Answer 12

it is a fossil fuel
it is formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in the ground (mud)

Question 13

describe the process of fractional distillation (specifically the process of separating crude oils hydrocarbons)

Answer 13

• the oil is heated until most has turned to gas. the gas then enters a fractionated column (the liquid bit drains of)
• in the column theres a temp gradient (hot at bottom, cool at top)
• longer hydrocarbons have higher boiling point so condense into liquid and drain out earlier on when there near the bottom. the shorter hydrocarbons have a lower boiling point so condense and drain out much later on, near the top of the column where it is cooler.
• you end up with 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 a similar boiling point.

Question 14

what is the main use of crude oil in the modern day?

Answer 14

oil provides fuel for most transport.

Question 15

what does cracking mean?

Answer 15

the splitting up of long chains of hydrocarbons

Question 16

why is cracking used?

Answer 16

short chained hydrocarbons are flammable so often long chains of hydrocarbons are broken down into short chains to be used for petrol and other fuels.

Question 17

what hydrocarbons does cracking often produce?

Answer 17

alkAnes and alkEnes. (alkEnes are a lot more reactive than alkanes)

Question 18

what are some different methods if cracking?

Answer 18

vaporising them- (catalytic cracking)

Question 19

what is catalyctic cracking?

Answer 19

splitting long chains of molecules apart on the surface of specs of hydrocarbons.

Question 20

what can be used to test for alkEnes and how is it done?

Answer 20

BROMINE water

• combine substances
• if no alkenes are present then the reaction will remain orange.
• if alkenes are present then the solution will go colourless.