alkenes

Question 1

What kind of reaction is cracking?

Answer 1

a thermal decomposition reaction

Question 2

process for catalytic cracking

Answer 2

1. heat long chain hydrocarbons to vaporise them
2. prepare hot powdered aluminium oxide ( to use as catalyst)
3. pass hydrocarbon vapour over powder
4. as hydrocarbons come into contact with the catalyst they will split apart into 2 smaller hydrocarbons

Question 3

process for steam cracking

Answer 3

1. heat long chain hydrocarbons to vaporise them
2. mix vaporised hydrocarbons with steam
3. heat them to a high temperature causing the long hydrocarbon chains to split apart into shorter ones

Question 4

what does the longer chain alkane break down into (there is 2 products)

Answer 4

a shorter alkane + a alkene

Question 5

what can alkenes be used for?

Answer 5

• to produce polymers (like plastic)

as the double bonds can break to form 2 more bonds

Question 6

what is the difference between alkanes and alkenes in terms of bonding and saturation?

Answer 6

alkanes only have a single bond whereas alkenes have a double bond
alkanes are saturated as every carbon atom is bonded to a hydrogen atom whereas alkenes are unsaturated because not every carbon is bonded to a hydrogen atom

Question 7

what do these difference mean in terms of reactivity?

Answer 7

alkenes are more reactive than alkanes and can react with bromine

Question 8

what is the test for alkenes?

what is a positive result?

Answer 8

bromine water

the bromine water will go from orange to colourless

Question 9

after you have formed ethanol by reacting ethene and water

how do you get rid of any excess ethene and water vapour (4 marks)

Answer 9

ethene has a low boiling point so if you cool down the mixture it will stay as a gas
while the water and ethanol will condense into a liquid then you use fractional distillation
during fractional distillation you heat the mixture of ethanol and water, the ethanol will boil first as it ha a slighter lower boiling point then water, it will evaporate up the fractionating column and condense into a separate beaker

Question 10

what conditions are needed for an alkene and water to react (2 marks)

Answer 10

catalyst

high temperatures

Question 11

what condition is needed for an alkene and hydrogen to react? (1 mark)

Answer 11

a catalyst

Question 12

What makes a good fuel?

Answer 12

Low boiling point

High volatility

Flammable

Question 13

When a fuel has been separated using fractional distillation, how could you test that it was pure?

Answer 13

Measure the boiling point of the substance.
Individual compounds have very specific boiling points. You could compare the boiling point of your fuel with the known value of the pure fuel.
A pure substance should boil over a very small temperature range. If your sample boils over a large range, it suggests that there are impurities present.

Question 14

Use your knowledge of the properties of a polymer to suggest which properties of a polymer are suited to the role of DNA?

Answer 14

Polymers can form very long chains. There is a huge amount of genetic information in an organism so having a polymer allows it to be stored in a few molecules.
Polymers are stable. The bonds of a polymer tend to be more stable than those of the individual monomers. This ensures that DNA is stable and can be passed on to children.