Alkanes

Question 1

Alkane definition

Answer 1

Saturated hydrocarbons that contain only carbon-carbon and carbon-hydrogen single bonds

Question 2

Saturated definition

Answer 2

Compounds contain single bonds only

Question 3

Hydrocarbons definition

Answer 3

Compounds containing carbon and hydrogen only

Question 4

Boiling point

Answer 4

BP increases with increasing C chain length because number of e- increases, so has strong van der waal forces

When amount of branches increases, but e- stays the same, BP decreases as:
- less surface contact
- weaker van der waal forces

Question 5

Fraction Definition

Answer 5

A mixture of compounds with similar boiling points and similar sized molecules

Question 6

What is the main source of hydrocarbons

Answer 6

crude oil

Question 7

Fractional Distillation

Answer 7

• compounds have different BP
• BP depends on length of compound
• hotter at bottom of column
• heavier molecules condense and collect at bottom

-IMF are broken

Question 8

Cracking

Answer 8

Larger fractions can be broken up into smaller fractions by cracking

Heavy fractions cracked as smaller chain molecules are in higher demand

Break C-C bonds to form smaller molecules

Question 9

Thermal cracking

Answer 9

High % alkenes

• high temperature ( 700-1200k)
• high pressure (7000kPa)

Question 10

Catalytic Cracking

Answer 10

High % branches alkanes/cycloalkanes

• high temperature (600k)
• slight pressure (100kPa)
• catalyst (zeolite)

Question 11

Complete combustion

Answer 11

In a plentiful supply of oxygen alkanes undergo complete combustion to form carbon dioxide and water.

C9H20 + 14O2 → 9CO2 + 10H2O

Question 12

Incomplete combustion

Answer 12

In a limited supply of oxygen, incomplete combustion may occur. In this case, carbon monoxide gas or solid carbon (soot) is made, along with water.

C12H26 + 12.5O2 → 12CO + 13H2O
C4H8 + 2O2 → 4C + 4H2O

Question 13

Chemicals produced during combusion

Answer 13

CO2:
Greenhouse gas- prevents earths heat escaping
Polar ice caps melt = flooding

H2O vapour:
Greenhouse gas- produces in large quantities as a result of combustion of HC

CO:
Poisonous/ toxic

Solid C:
Damages the lungs- harder to breathe for asthma sufferers

Question 14

Sulphur dioxide

Answer 14

S(s) + O2(g) → SO2(g)
This gas dissolves in rainwater forming a very acidic solution of sulphuric acid, known as acid rain.

SO2(g) + 0.5 O2(g) + H2O(l) → H2SO4(l)
This causes various problems, including erosion of buildings and killing of plants and trees, and killing of fish through contamination of lakes.

Question 15

Oxides of nitrogen (NOx)

Answer 15

the high temperatures in the car engines cause some of the nitrogen to react with the oxygen to produce nitric oxide (NO), nitrogen dioxide (NO2) and NOx.
N2(g) + O2(g) → 2NO(g)
2NO(g) + O2(g) → 2NO2(g)

Nitrogen dioxide (NO2) also dissolves in rainwater to form an acidic solution of nitric acid (HNO3) and contributes to the problem of acid rain.

4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(g)

Question 16

Unburnt Hydrocarbons

Answer 16

They are toxic and can cause cancer if breathed in.

Question 17

Reducing pollution: flue gas desulfurisation

Answer 17

In desulfurisation the acidic sulphur dioxide gas is neutralised by an alkali.

two methods of desulfurisation:
1) CaO(s) + 2H2O(l) + SO2(g) + 0.5 O2 → CaSO4.2H2O(s)
2) CaCO3(s) + 0.5 O2(g) + SO2(g) → CaSO4(s) + CO2(g)

Question 18

Reducing pollution: Catalytic converters

Answer 18

Honeycomb structure made of platinum and rhodium metals, which are the catalysts.
The honeycomb structure increases the surface area, increasing the rate of the reactions:

Removal of carbon monoxide and nitrogen monoxide:
2NO(g) + 2CO(g) → N2(g) + 2CO2(g)

Removal of unburned hydrocarbons and nitrogen monoxide
C8H18 + 25NO → 8CO2 + 9H2O + 12.5N2