Chapter 15: Alkanes and Alkenes

Question 1

Name all the alkanes, their molecular formula, and their general formula

Answer 1

1. Methane CH3
2. Ethane C2H6
3. Propane C3H8

General formula: CnH2n+2

Question 2

What reaction does alkanes do

Answer 2

1. Reacting with halogens in the presence of ultra-violet light
   - Hydrogen is substituted with a halogen atom

Question 3

Name all the alkenes, their molecular formula, and their general formula

Answer 3

1. Ethene C2H4
2. Propene C3H6

General formula CnH2n

Question 4

What reactions does alkenes do

Answer 4

1. Bromination (testing for saturation)
   - When alkene is added into bromine solution, the reddish brown solution decolourises rapidly and a colourless liquid is formed

• Alkane: No change

Saturation
Alkene: unsaturated (reactive)
Alkane: saturated (unreactive)

2. Hydrogenation
   - React with hydrogen to form alkanes

• For manufacture of margarine. The more hydrogen, the more solid margarine is

Question 5

Define polyunsaturated

Answer 5

Polyunsaturated is when there is more than one carbon-carbon double bonds

Question 6

What are the products when alkane and alkene undergoes complete combustion

Answer 6

Alkane + oxygen —> Carbon dioxide + water

Alkene + oxygen —-> Carbon dioxide + water

Complete combustion: Reacting with sufficient oxygen in the air

Question 7

What are the products when alkane and alkene undergoes incomplete combustion

Answer 7

Alkane + oxygen —> Carbon monoxide + carbon + water

Alkene + oxygen —-> Carbon monoxide + carbon + water

Incomplete combustion: Reacting with insufficient oxygen in the air

Question 8

What are the reactions does alkanes and alkenes do

Answer 8

Alkane: Substitution (no more carbon atom to add anymore) (saturated)
Alkene : Addition (unsaturated)

Question 9

What are the physical properties of alkanes and alkenes (covalent compounds)

Answer 9

1. Low melting and boiling point
2. Insoluble in water
3. Soluble in organic solvents
4. Does not conduct electricity in any states

Question 10

What are the physical trends in alkanes and alkenes

Answer 10

As molecular masses increases…

1. Melting and boiling point increases
2. Viscosity increases
   3.Flammability decreases

Question 11

What are the characteristics of the homologues series

Answer 11

1. Same chemical properties (same group)
2. Same general formula
3. Same functional group
4. Shows gradual change in their physical properties