Alkanes

Question 0

State the meaning of both the words SATURATED and HYDROCARBON as applied to the term saturated hydrocarbon.

Answer 0

An organic compound that contains only carbon and hydrogen single bonds.

Question 1

The main source of Alkanes is…

Answer 1

Crude oil.

Question 2

Boiling points of Alkanes increase as…

Answer 2

The chain length increases.

Question 3

Why do Alkanes with branched chains have lower boiling points than the corresponding straight chain Alkanes?

Answer 3

The branched Alkanes have weaker intermolecular forces due to less surface contact.

Question 4

Why are Alkanes insoluble in water?

Answer 4

Alkanes are almost non-polar and the intermolecular forces between the water molecules (hydrogen bonds) are much stronger than the intermolecular forces between Alkanes (VdW).

Question 5

Are Alkanes reactive or unreactive?

Answer 5

They are relatively unreactive due to having strong carbon-carbon and carbon-hydrogen bonds.

Question 6

Name a process used to separate Octane from a mixture containing several different Alkanes.

Answer 6

Fractional Distillation.

Question 7

State what is meant by the term Cracking.

Answer 7

Cracking is the breakdown of large hydrocarbon molecules into smaller, more useful hydrocarbon molecules.

Question 8

Thermal Cracking tends to produce..

Answer 8

A high proportion of Alkenes.

Question 9

Conditions for Thermal Cracking =

Answer 9

High Temperature: 700K-1200K.

High Pressure: 7000kPa.

Question 10

Catalytic Cracking takes place at a…

Answer 10

Low Temperature (around 720K).
Low pressure.
Using a Zeolite catalyst consisting of Silicon Dioxide and Aluminium Oxide.

Question 11

What are the products of complete combustion of alkanes?

Answer 11

Carbon Dioxide and Water.

Question 12

What are the products of incomplete combustion of alkanes?

Answer 12

Carbon Monoxide and Water.

Question 13

Why are Alkanes polar?

Answer 13

Alkanes are almost non-polar because the electronegativities of Carbon and Hydrogen are so similar.

Question 14

The only Intermolecular forces between Alkanes are..

Answer 14

VdW.

Question 15

Is the Combustion of Alkanes endothermic or exothermic?

Answer 15

Exothermic.

Question 16

Name 3 greenhouse gases.

Answer 16

Methane, Carbon Dioxide and Water Vapour.

Question 17

What are the main products of Catalytic Cracking?

Answer 17

Branched alkanes, cycloalkanes and aromatic compounds. Motor fuels.

Question 18

Name the catalyst used in Catalytic Cracking.

Answer 18

Zeolite.

Question 19

Write an equation for the incomplete combustion of C8H18 to form Carbon Monoxide and Water only.

Answer 19

C8H18 + 8.5O2 = 8CO + 9H2O

Question 20

Why is a Catalytic Converter used?

Answer 20

To remove Carbon Monoxide from the exhaust gases in a car.

Question 21

Identify a catalyst used in the catalytic converter.

Answer 21

Rhodium or Platinum.

Question 22

State why the water produced in the exhaust gases may contribute to global warming.

Answer 22

Water vapour is a greenhouse gas.

Question 23

Write an equation to show how Nitrogen Monoxide in the air is converted into Nitrogen Dioxide.

Answer 23

2NO + O2 = 2NO2.

Question 24

Deduce an equation to show how Nitrogen Dioxide reacts with Oxygen and Water to form Nitric Acid.

Answer 24

2NO2 + 1.5O2 + H2O = 2HNO3.

Question 25

Oxides of Nitrogen are also produced during the combustion of paraffin in air.

Explain how these oxides of Nitrogen are formed.

Answer 25

High temperature. Nitrogen and Oxygen reacting in the air.

Question 26

Explain why the melting point of Dodecane is higher than the melting point of the straight-chain Alkanes produced by cracking dodecane.

Answer 26

Dodecane has a longer chain length/size and so it has more Van der Waals forces of attraction and therefore more energy is required to overcome this.

Question 27

Why does Thermal Cracking need a high temperature?

Answer 27

To break the carbon-carbon bonds (and form shorter chain Alkane and an Alkene).

Question 28

What are the two properties of a Zeolite Catalyst?

Answer 28

1. They are acidic

2. They have a honeycomb structure with an enormous surface area.

Question 29

What does Sulphur Dioxide contribute to?

Answer 29

Acid rain - it reacts with water vapour and oxygen to form Sulfuric acid.

Question 30

What is the process of removing Sulphur in chimneys called and what does it involve?

Answer 30

Flue gas desulfurisation - Calcium Oxide (CaO) or limestone (CaO₃) is used to absorb Sulphur dioxide, producing gypsum (CaSO₄) which is used as plaster.

Question 31

How does Carbon Dioxide trap heat in the Earth’s atmosphere?

Answer 31

Visible radiation (sunlight) penetrates the atmosphere. Infra-red radiation is emitted by the Earth - this is trapped by the greenhouse gases in the atmosphere and cannot escape.

Question 32

What do unburnt hydrocarbons contribute to?

Answer 32

Photochemical smog and health problems.

Question 33

Carbon Monoxide is a ______ gas.

Answer 33

Toxic/Poisonous.

Question 34

What do Carbon particulates contribute to?

Answer 34

Asthma and cancer.

Question 35

What happens to the harmful products in the Catalytic Converter?

Answer 35

They react with each other to produce less harmful products:

Carbon Monoxide + Nitrogen Oxide → Nitrogen + Carbon Dioxide.

Hydrocarbon + Nitrogen Oxide → Nitrogen + Carbon Dioxide + Water.

Question 36

Outline the essential features of the fractional distillation of crude oil that enable the crude to be separated into fractions.

Answer 36

The fractions separate due to having different boiling points.
There is a temperature gradient - the column is cooler at the top.
The vapours pass up the tower via a series of trays containing bubble caps until they arrive at a tray that is cool enough to condense the vapour.
Boiling point depends on the chain length/size.
The molecules with higher boiling points are at the bottom of the column (heavier).

Question 37

What is meant by the term fuel?

Answer 37

A material such as coal, gas, or oil that is burned to produce heat or power.