Organic Chemistry Year11

Question 1

what 2 elements make up hydrocarbons

Answer 1

hydrogen and carbon

Question 2

state the pattern in the properties of hydrocarbons

Answer 2

as the chain gets longer:

• more viscous (sticky and thick)
• less volatile (higher B.P)
• less flammable

Question 3

compare the viscosity, boiling point and flammability of C5H12 and C10H22

Answer 3

C5H12 is less viscous than C10H22
C5H12 has a lower boiling point C10H22
C5H12 has higher flammability C10H22

Question 4

what is the chemical formula of butane

Answer 4

C4H10

Question 5

what is the general formula to work out the chemical formula of any alkane

Answer 5

C(n)H(2n+2)

Question 6

what is the general equation of the combustion of any hydrocarbon

Answer 6

hydrocarbon + O2 –> CO2 + H2O (+energy)

Question 7

what are the products are the combustion of any hydrocarbon

Answer 7

carbon dioxide and water

Question 8

how is crude oil formed?

Answer 8

its a fossil fuel so is formed out of dead plant/animal matter (mostly plankton) over millions years compressed by immense heat and pressure

Question 9

describe the process of fractional distillation for fractioning crude oil

Answer 9

• oil is heated until most of it is a gas & entered into the fractioning column
• there’s a temp gradient (hotter at bottom;colder at top)
• the longer chains have higher b.p so condense into a liquid early on & flow out the column
• shorter chains float to the top as they have lower b.p so condense later on
• oil is seperated into fractions which all have uses ie petrol/kerosene/diesel

Question 10

what is cracking and what does it do?

Answer 10

• its a thermal decomposition reaction which breaks down molecules by heating them
• used to produce fuels ie petrol and alkenes

Question 11

where are the shortest carbon chains found in the fractional distillation column

Answer 11

at the top (lower b.p)

Question 12

give 3 products that can be made from crude oil

Answer 12

petrol/kerosene/diesel

Question 13

what is the difference between an alkane and an alkene

Answer 13

-

Question 14

how does catalytic cracking work

Answer 14

• long chain hydrocarbons are heated until they are a gas
• the gas is passed over a hot powdered aluminium oxide catalyst
• hydrocarbon molecules are split apart by the surface of the catalyst specks

Question 15

what is steam cracking

Answer 15

• long chain hydrocarbons are heated until they are a gas

- gas is mixed with steam then heated to a v. high temp which cause the hydrocarbon molecules to be split apart