3.2 Alkanes

Question 1

Definition of an alkane

Answer 1

Is a saturated hydrocarbon

Question 2

Properties of alkanes

Answer 2

Non polar - can’t dissolve in water
Has weak Vdw forces so low boiling point
Having chain isomers of alkanes lowers the boiling point

Question 3

What is crude oil

Answer 3

Natural unrefined substance of organic molecules

Question 4

Properties of shorter chain hydrocarbons

Answer 4

lower boiling point
More volatile
More flammable
Less viscous

Question 5

Why is cracking done?

Answer 5

To meet the demand of the low supply of short chain hydrocarbons

Question 6

How is thermal cracking done?

Answer 6

With a high temperature
high pressure
Creates free radicals which eventually produce an alkene and an alkane

Question 7

How is catalytic cracking done

Answer 7

Low temp and Low pressure
Zeolite is used as the catalyst
Produces- chain isomers of alkanes
and cycloalkanes

Question 8

What are the pollutants of combustion

Answer 8

Carbon monoxide-poisionous gas
Carbon particulates- cause asthma
carbon dioxide and water vapour - green house gases
sulfur dioxide - acid rain
Nitrogenous oxide

Question 9

Reaction for complete combustion

Answer 9

Hydrocarbon+ oxygen = carbon dioxide and water

Question 10

What is flue gas desulphurisation

Answer 10

Sulphur dioxide reacts with the environment to create sulphuric acid
This is stopped with the reaction of Calcium oxide
to create calciumsulfate which is less harmful

Question 11

What do catalytic converters do?

Answer 11

The harmful gases from a car engine pass through the converter
This makes the gases react with themseleves to create less harmful gases

Question 12

Global warming effect

Answer 12

Infra red from the sun is trapped by greenhouse gases

This increases temp which means more water vapour in the air means more Greenhouse gases in air so more global warming

Question 13

Outline the essential features of the fractional distillation of crude oil that enables it to be separated into fractions

Answer 13

Fractions or hydrocarbons have different boiling points bp depends on size of molecules / Mr / chain length

There is a temperature gradient in the column – it is cooler at the top of the column (or vice versa)

Higher bp / molecules or the heavier molecules are at the bottom of the column (or vice vers

Question 14

Give two reasons why boilers are designed to ensure complete combustion

Answer 14

Prevent carbon monoxide which is toxic
More energy sufficent

Question 15

Why do alkenes have more commercial value then alkanes ?

Answer 15

Can be made into polymers