t7- organic chemistry (1)

Question 1

how does fractional distillation work
4 steps

Answer 1

1.heated crude oil enters fractionating column which is hot at bottom and cool at top
2.vapours rise up the column
3.vapurs condense when they become cool enough-they condense at different fractions depending on their BP
4.liquids come out the column at different heights

Question 2

describe the amount of time spent by different chains in fractional distillation
2 points and examples

Answer 2

-short chains have lower BP so they stay as a gas for longer
eg.diesel, petrol, kerosene
-longer chains have higher BP so they quickly condense back into a liquid and drain out of the column early on
eg. bitumen, heavy fuel oil

Question 3

4 characteristics of small molecules

Answer 3

-low BP
-very volatile
-flows easily
-ignites easily

Question 4

4 characteristics of large molecules

Answer 4

-high BP
-not very volatile
-doesn’t flow easily
-doesn’t ignite easily

Question 5

what is crude oil formed from

Answer 5

formed naturally from remains of plants/animals like plankton
it’s finite

Question 6

equation for cracking

Answer 6

long chain alkane-> shorter alkane+alkene

Question 7

what type of reaction is cracking

Answer 7

thermal decomposition reaction

Question 8

what 2 things cracking produce

Answer 8

alkenes which are useful for feedstock and petrochemical industry
shorter chains which are more useful and in high demand

Question 9

what is steam cracking

Answer 9

-long molecules heated to vapourisation
-vapours mixed with steam and are heated to very high temperatures

Question 10

what is catalytic cracking

Answer 10

-long molecules heated to vapourisation
-vapour is passed over zeolite catalyst which contains aluminium oxide

Question 11

describe the 3 trends as alkane chain length increases

Answer 11

-BP increases- methane, ethane, propane, butane have low BP, so are gases at room temp
-viscosity increases(short alkanes are volatile)
-flammability decreases

Question 12

describe use of alkanes in combustion

Answer 12

-fuel
-alkanes release lots of energy when burned with oxygen (complete combustion)

Question 13

what are alkenes

Answer 13

unsaturated hydrocarbons with a C=C double bond

Question 14

how to test for alkenes

Answer 14

-bromine water, as they’re more reactive than alkanes as they’re unsaturated
-bromine changes from orange to colourless

Question 15

describe hydrogenation as a reaction of alkenes

Answer 15

alkene+hydrogen->alkane
-double bond opens up to add extra hydrogen

Question 16

describe hydration as a reaction of alkenes
and conditions needed

Answer 16

alkene+water->alcohol
-requires high temp and catalyst
eg. ethene+steam->ethanol

Question 17

describe halogens in a reaction of alkenes

Answer 17

alkene+halogen->halogenalkane
eg.ethene+bromine->dibromoethane