3.2 Alkanes

Question 1

Saturated

Answer 1

Compounds with single bonds only

Question 2

Hydrocarbons

Answer 2

Compounds with carbon and hydrogen only

Question 3

General formula

Answer 3

CnH2n+2

Question 4

Factors affecting boiling point of alkanes

Answer 4

Chain length
Number of branches

Question 5

Trend of boiling point with increasing carbon chain length

Answer 5

Boiling point increases
More molecules
Strength of induced dipole dipole between molecules gets stronger

Question 6

Trend of boiling point with increasing number of branches

Answer 6

Boiling point decreases
More branches
More surface contact area
Induced dipole dipole between molecules stronger

Question 7

Crude oil

Answer 7

Mixture of hydrocarbons with different chain lengths

Question 8

Fraction

Answer 8

Mixture of compounds with similar BP and size of molecules

Question 9

Features of fractional distillation

Answer 9

• Crude oil heated to vaporise and enters column
• Hydrocarbons have different BP, depending on size, Mr and chain length
• Cooler at the top and hotter at the bottom
• Larger molecules condense at the bottom

Question 10

Fractions in column

Answer 10

Gasoline
Naphtha
Paraffin
Diesel
Lubricating oil
Bitumen

Question 11

Purpose of cracking

Answer 11

To make alkenes and shorter chain molecules

Question 12

Thermal cracking conditions

Answer 12

High temp : 700-1200K
High pressure : 7000KPa

Question 13

Products of thermal cracking

Answer 13

One alkane
Many alkenes

Question 14

Catalytic cracking conditions

Answer 14

High temp : 720K
Slight pressure : 100KPa
Catalyst: Zeolite

Question 15

Products of catalytic cracking

Answer 15

High percentage of branched alkanes and cycloalkanes

Question 16

Complete combustion of nonane

Answer 16

C9H20 + 14O2 –> 9CO2 + 10H2O

Question 17

Incomplete combustion of dodecane to produce gases only

Answer 17

C10H22 + 21/2O2 –> 10CO + 11H2O

Question 18

Incomplete combustion of but-1-ene to produce a solid

Answer 18

C4H8 + 2O2 –> 4C + 4H2O

Question 19

What is carbon dioxide

Answer 19

Greenhouse gas

Question 20

What is water

Answer 20

Greenhouse gas

Question 21

What is carbon monoxide

Answer 21

Poisonous gas

Question 22

What does solid carbon do

Answer 22

Damages the lungs

Question 23

Equation for the formation of acid rain

Answer 23

SO2 + 1/2O2 + H2O –> H2SO4

Question 24

Equation for the formation of sulphur dioxide

Answer 24

S + O –> SO2

Question 25

Equation of nitrogen dioxide dissolving in rainwater

Answer 25

4NO2 + 2H2O + O2 –> 4HNO3

Question 26

What is a catalytic converter

Answer 26

A honeycomb structure made of platinum and rhodium

Question 27

What does a catalytic converter do

Answer 27

Converts some of the harmful gases in a car exhaust into less harmful gases
Increases the surface area, increasing the rate of reactions

Question 28

What are the problems with unburned hydrocarbons

Answer 28

They are toxic and ca n. cause cancer if breathed in

Question 29

Desulfurisation

Answer 29

Acidic sulphur dioxide neutralised by alkali

Question 30

Removal of carbon and nitrogen monoxide equation

Answer 30

2NO + 2CO –> N2 + 2CO2