16. Hydrocarbons

Question 1

Homologous Series

Answer 1

A homologous series consists of a family of compounds with the same general formula. They show similar chemical properties because they have the same functional group

Question 2

General characteristic of a homologous series

Answer 2

1. Same functional group
2. Similar chemical properties
3. As we go down the series, each member of the series has an additional CH2
4. There is a gradual change in their physical properties

Question 3

Naming organic compounds

Answer 3

1. meth
2. eth
3. prop

Question 4

Formula and names of alkanes

Answer 4

1. Alkanes are hydrocarbons that contain only carbon-carbon single bonds
2. CnH2n+2
3. They are saturated hydrocarbons

Question 5

Formula and names of Alkenes

Answer 5

1. Alkenes are hydrocarbons that contain a Carbon-Carbon double bond
2. General formula: CnH2n
3. They are unsaturated hydrocarbons

Question 6

physical properties of alkanes

Answer 6

1. Alkanes are substances with weak forces of attraction hence in general they have low melting and boiling point
2. The MP/BP gradually increases down the homologous series
3. Alkanes become more viscous as their molecule sizes increases
4. Alkanes are insoluble in water but soluble in organic solvents

Question 7

Chemical properties of alkanes

Answer 7

1. Alkanes undergo combustion when oxygen is present. With insufficient oxygen, carbon monoxide will be produced instead of carbon dioxide
2. Alkanes react with halogens in the presence of UV light. This is where the Hydrogen atom is being replaced by the halogen

Question 8

Physical properties of alkenes

Answer 8

1. Their melting and boiling point is extremely low due to the weak forces of attraction, it gradually increases down the homologous series
2. Alkenes become more viscous as their molecules increase in size
3. They are insoluble in water but soluble in organic solvents

Question 9

Chemical properties of Alkenes

Answer 9

1. Combustion happens just like the alkenes
2. Addition reactions where C-C double bonds will become C-C single bonds
3. Hydrogenation: Alkenes react with hydrogen under the conditions of a temperature of 150 degrees and the presence of nickel catalyst
4. Bromination: Alkenes react with halogens
5. Polymerisation is where the monomer reacts with each other to form a long polymer. However, the conditions are: High temperature and pressure, catalyst.

Question 10

Describe the process and importance of cracking

Answer 10

1. Cracking is a process in which larger hydrocarbon molecules, usually alkenes, are broken into smaller hydrocarbon molecules
2. Cracking converts the less useful components to more useful substances.

Question 11

Test for unsaturation

Answer 11

1. Aqueous bromine remains brown if alkenes is present
2. Aqueous bromine decolorised if alkanes is present