Alkanes

Question 1

what is an alkane?

Answer 1

staurated hydrocarbons containing a single C-H

Question 2

Are their bonds polar? Why/why not?

Answer 2

Nonpolar- carbon and hydrogen have similar electronegativities

Question 3

Intermolecular forces? Why?

Answer 3

Only van der Waals forces of attraction - bonds are
non-polar

Question 4

Solubility in water? why?

Answer 4

Insoluble because hydrogen bonds in water are stronger than alkanes’ van der
Waals forces of attraction

Question 5

How reactive are alkanes?

Answer 5

Very unreactive

Question 6

Which reactions will alkanes undergo?

2.3 Combustion of alkanes

Answer 6

Combustion and reaction with halogens

Question 7

What is crude oil? How is it formed? Is it renewable?
Why?

2.1 Fractional distillation of crude oil

Answer 7

Mixture of fractions (hydrocarbons with similar boiling points and properties)
Formed at high temperatures and pressures deep below earth’s surface over millions of years
→ therefore non-renewable

Question 8

What is fractional distillation/how does it work?

2.1 Fractional distillation of crude oil

Answer 8

Crude oil heated until mostly vapourised
Passed into a fractionating tower that is cooler at the top than the bottom
Liquid fractions are piped off at the bottom
Vapours rise up the column and - via trays and bubble caps - condense when temperature < their boiling point
Shortest chain hydrocarbons condense at the top as they have the lowest boiling points

Question 9

What is fracking and how is it done?

2.2 Modification of alkanes by cracking

Answer 9

Natural gas held within shale rock
Drill into shale, force pressurised water and sand into rock to fracture it, Collect gas
HCI and methanol added to break up shale and prevent corrosion

Question 10

Pros/cons of fracking?

2.2 Modification of alkanes by cracking

Answer 10

Advantages - gas supply for many years, reduces imported gas and electricity
Disadvantages - lots of traffic to local area, concern about amount of water used, chemical additives can pollute water supplies, can cause small earthquakes, combust CHA → CO2 → global warming

Question 11

Why are alkanes cracked?

2.2 Modification of alkanes by cracking

Answer 11

To turn a long chain alkane, with is not very economically valuable, into a shorter chain alkane (more economically valuable as can be used as a fuel) and an alkene (more reactive, starting point for many products)

Question 12

What are the conditions for thermal cracking?

2.2 Modification of alkanes by cracking

Answer 12

700-1200 K temperature
Up to 7000 kPa pressure

Question 13

What is incomplete combustion and what products are formed in the case of alkanes?

2.3 Combustion of alkanes

Answer 13

Combustion in a limited supply of oxygen
CO - carbon monoxide - poisonous
C - carbon - particulates - soot - global dimming

Question 14

Which type of hydrocarbons are most likely to undergo incomplete combustion?

2.3 Combustion of alkanes

Answer 14

Longer chains

Question 15

What is the environmental impact of soot (carbon)?

2.3 Combustion of alkanes

Answer 15

asthma, cancer, global dimming

Question 16

What are flue gases?

2.3 Combustion of alkanes

Answer 16

Gases given out by power stations

Question 17

What are catalytic converters made up of?

2.3 Combustion of alkanes

Answer 17

Ceramic honeycomb coated with platinum, palladium and rhodium (Pt, Pd and Rh) metals

Question 18

catalytitic cracking

2.3 Combustion of alkanes

Answer 18

Lower temperatures around 720 K are used along with normal pressure, but a zeolite catalyst is needed to compensate fo these less harsh conditions.

Question 19

2.4 Chlorination of alkanes