Alkanes

Question 1

what is the formula for ozone?

Answer 1

O3

Question 2

where is the ozone situated and what is its purpose?

Answer 2

• between mesosphere and stratosphere

- absorbs UV radiation

Question 3

what are CFCs and how do they affect the ozone layer?

Answer 3

• chlorofluorocarbons
• rise to stratosphere before UV light provides energy to break C-Cl bonds
• forms Cl radicals which converts ozone into oxygen

Question 4

what is the purpose of the montreal protocol?

Answer 4

prevents thinning of ozone layer and builds it up again by banning uses of CFCs

Question 5

name four uses of CFCs

Answer 5

• coolants in frides
• propellants in aerosols
• dry cleaning solvents
• degreasing circuit boards

Question 6

what are alternatives to CFCs?

Answer 6

HFCs - hydrofluorocarbons - no free radicals formed because no chlorine

Question 7

what is crude oil?

Answer 7

mixture composed of straight and unbranched alkanes`

Question 8

what is the origin of alkanes?

Answer 8

• fossil fuels millions of years ago - breakdown of plants and animals

Question 9

how is crude oil separated?

Answer 9

fractional distillation in a fractionating tower

Question 10

what is each fraction?

Answer 10

a mixture of hydrocarbons with same boiling point

Question 11

name the fractions

Answer 11

gases
gasoline
kerosene
diesel oil
lubricating oil
fuel oil
bitumen

Question 12

what is the use of gases?

Answer 12

fuel on site

Question 13

what is the use of gasoline?

Answer 13

petrol for cars

Question 14

what is the use of kerosene?

Answer 14

jet fuel/ lighting

Question 15

what is the use of diesel oil?

Answer 15

lorries/taxis

Question 16

what is the use of lubricating oil?

Answer 16

engine oil/ candles

Question 17

what is the use of fuel oil?

Answer 17

ships/ power stations

Question 18

what is the use of bitumen?

Answer 18

tar on roads

Question 19

explain the process of fractional distillation

Answer 19

• crude oil is vaporised
• different hydrocarbons have different bp
• lighter shorter chain hydrocarbons travel further up column and have lower bp so condense at the top
• long chain hydrocarbons condense at the bottom

Question 20

what is cracking?

Answer 20

breakdown of long chain alkanes into shorter alkanes

Question 21

why do we use cracking?

Answer 21

• shorter chain products are more economically valuable than long chain products
• in order to meet the demand cracking is used to break long chain alkanes down
• produces more useful short chain alkanes - used for petrol
• also produces alkenes which are used in polmers for plastics

Question 22

what are the two types of cracking?

Answer 22

• thermal

- catalytic

Question 23

why do alkanes require harsh conditions to break them down?

Answer 23

very unreactive

Question 24

how does thermal cracking work and what conditions are needed?

Answer 24

• high temp: 700-1200K
• high pressure: up to 7000 kPa
  carbon-carbon double bond breaks producing free radicals which combine to form alkane and alkenes
• produces high proportion of alkenes

Question 25

why is thermal cracking undergone a short time?

Answer 25

to avoid decomposition

Question 26

what does catalytic cracking produce?

Answer 26

motor fuels - branched alkanes, cycloalkanes

Question 27

what catalyst is used in catalytic cracking?

Answer 27

zeolite - silicon dioxide and aluminium oxide

Question 28

what conditions are used in catalytic cracking?

Answer 28

lower temp: 720K

lower pressure of 7atm

Question 29

what is the test for carbon-carbon double bond?

Answer 29

decolourises bromine water