3.3.2 - ALKANES

Question 1

What is crude oil and how is it formed

Answer 1

• a mixture of different length hydrocarbons
  1. Sediment builds up on remains of plankton, increasing the pressure
  2. Compressed biomass over millions of years forms crude oil

Question 2

What is fractional distillation used for and how does it work

Answer 2

• used to separate alkanes based on their B.P
  1. Heat up crude oil
  2. Crude oil into the column, which has a temperature gradient
  3. Hydrocarbons condense at their boiling point
  4. Shorter chains condense towards top, due to low B.P
  5. Longer chains condense towards bottom, due to high B.P

Question 3

What is a “fraction”

Answer 3

A mixture of compounds with similar boiling points

Question 4

State features of long vs short chain alkanes

Answer 4

LONG: darker, more viscous, higher B.P (stronger VdW’s)
SHORT: lighter, more flammable, lower B.P

Question 5

State features of thermal cracking

Answer 5

• 900°C (high temp)
• 70atm (high pressure)
• no catalyst
• produces alkanes (ADV)

Question 6

State features of catalytic cracking

Answer 6

• 450°C (lower temp)
• 1-2atm (low pressure)
• zeolite catalyst
• produces: motor fuels, aromatic hydrocarbons

Question 7

Which form of cracking is favoured and why?

Answer 7

• catalytic cracking over thermal
• less dangerous, due to low pressure
• less energy, due to low temp, so is cheaper
• zeolite catalyst can be reused

Question 8

• what is cracking
• why is it come

Answer 8

• breaking C-C bonds
• produces shorter chain alkanes (e.g. petrol), which are higher in demand
• produces alkanes, which are used to make plastics

Question 9

What is produced in complete combustion

Answer 9

• CO2
• H2O

Question 10

What is produced in incomplete combustion

Answer 10

• C or CO
• H2O

Question 11

Why are alkanes good fuels

Answer 11

• burn readily in the presence of O2
• reaction is highly exoteric
• release lots of energy

Question 12

How is Sulfur Dioxide formed and why is it a pollutant

Answer 12

• coal + oil/petrol react with O2 when burnt
• forms acid rain, damaging aquatic life, plants, erodes statues

Question 13

How are NO and NO2 formed and why are they pollutants

Answer 13

• Nitrogen in the air (makes up 78%) reacts with O2 inside engines
• produces acid rain
• damages aquatic life, plants
• erodes statues

Question 14

How is CO2 formed and why is it a problem

Answer 14

• complete combustion
• greenhouse gas
• traps radiation inside Earths atmosphere

Question 15

How are CÓ and C formed and why are they problems

Answer 15

• incomplete combustion
• CO = poisonous
• C = respiratory problems