Hydrocarbons

Question 1

What are alkanes?

Answer 1

Saturated hydrocarbons with the general formula CnH2n+2

Question 2

What are saturated hydrocarbons?

Answer 2

Compounds of carbon and hydrogen only in which the carbon-carbon bonds are all single covalent bonds, resulting in the maximum number of hydrogen atoms in the molecule.

Question 3

Why are alkane combusted?

Answer 3

1. To generate electricity in power stations
2. To heat homes and cooking
3. To provide energy needed in industrial processes
4. To provide fuel for vehicles.

Question 4

Equation of complete combustion of Alkane and state how much oxidation occurs.

Answer 4

Alkane + Oxygen —–> CO2 + Water

All the carbon is oxidized to carbon dioxide and all the hydrogen is oxidized to water.

Question 5

Equation for incomplete combustion of alkane and state why does incomplete combustion of alkane occur?

Answer 5

Alkane + Oxygen —–> Carbon monoxide + carbon (soot) + water

This occurs when alkane is mixed with a limited supply of oxygen, causing a partial oxidation of carbon which forms CO.

Question 6

What type of gas is CO and why is carbon monoxide a pollutant?

Answer 6

It is an odourless, toxic gas.
CO binds with the haemoglobin in red blood cells. So, oxygen can no longer bind to hemoglobin thus enough oxygen cannot be transported around the body.
High levels of CO can also be fatal.

Question 7

Which gases are produced alongside CO during incomplete combustion of alkane.

Answer 7

Oxides of nitrogen (NO and NO2)

Question 8

How does a catalytic converter reduce traffic emission?

Answer 8

1. Oxidation of carbon monoxide to form carbon dioxide
   2CO + 2NO —> 2CO2 + N2
   or,
   2CO + O2 —> 2CO2
2. Reduction of nitrogen oxides to form harmless nitrogen gas
   2CO + 2NO —> 2CO2 + N2
3. Oxidation of unburnt hydrocarbons to form carbon dioxide and water.

Question 9

What are hydrocarbons?

Answer 9

Hydrocarbons are compounds that are made up of carbon and hydrogen atoms ONLY

Question 10

What is a functional group?

Answer 10

A functional group is an atom or a group of atoms in an organic molecule, which determines the physical and chemical properties of the molecule

Question 11

Criteria for oxidation and reduction

Answer 11

Oxidation is
1. addition of oxygen
2. Removal of hydrogen
3. Loss of electrons
4. Increase in oxidation number

Reduction is
1. Removal of oxygen
2. Addition of hydrogen
3. Gain of electrons
4. Decreased oxidation number

Question 12

Redox equations: use of [O] and [H]

Answer 12

[O] means one atom of oxygen from an oxidizing agent

[H] means one atom of hydrogen from a reducing agent.

Question 13

free-radical substitution reaction:

Answer 13

A free-radical substitution reaction is a reaction in which halogen atoms substitute for hydrogen atoms in alkanes

Question 14

How is oxides of nitrogen cause harm?

Answer 14

They contribute to the problem of acid rain as they dissolve in the moisture. Acid rain can kill trees and aquatic animals in lakes as the pH of the lake is disrupted.
It can also erode limestone buildings and statues as well as corrode metals like iron.

Question 15

How does the ratio of Carbon to Hydrogen affect their probability of combustion?

Answer 15

Probability of combustion decreases as the C:H ratio increases.

Question 16

How are oxides of nitrogen formed?

Answer 16

At high temperature in a car engine, nitrogen and oxygen in the air react together to form oxides of nitrogen.

Question 17

How does nitrogen cause acid rain?

Answer 17

Oxides of nitrogen escape into the atmosphere where they dissolve in moisture and form nitric acid which can fall as acid rain.

Question 18

Equation for nitrogen dioxide and water.

Answer 18

NO2 + H2O —> HNO2 (nitrous acid) + HNO3 (nitric acid)

Question 19

Positively charged electrophile examples:

Answer 19

R+
CH3+
C2H5+
H3C-CH2-CH2+
Cl+
Br+
I+
H+
NO2+
H3C=O+

Question 20

How does the bond between bromine become polar when reacting with an alkene?

Answer 20

Bromine molecule does not have a polar bond however, as it approaches the C-C double bond, the pi bond in the C-C double bond repels the electrons in the bromine molecule. This induces bond polarity causing the Br atom closer to the C-C double bond to become slight positive and the other one to be slightly negative.

Question 21

Conditions of electrophilic addition of hydrogen bromide and an alkene.

Answer 21

Happens at room temperature.

Question 22

Conditions for free radical substitution reaction in alkane.

Answer 22

It requires ultraviolet light (sunlight) for this reaction to occur.