Module 4 - Alkanes

Question 1

5 properties of alkanes

Answer 1

1.Nonpolar-similar electronegativities
2.London forces- nonpolar
3.Insoluble- hydrogen bonds stronger than induced forces
4.Very unreactive
5.Tetrahedral- 109.5

Question 2

What is the shape and bond angle for alkanes

Answer 2

Tetradehedral 109.5

Question 3

What is the trend for the boilling points for alkanes, explain.

Answer 3

Boiling points increases as you increase the cabon chain length
Number of electrons increase/ Increased SA
Stronger London forces
More energy req to overcome these forces

Question 4

What type of bonds do alkanes have

Answer 4

sigma bonds

Question 5

Defintion of sigma and pi bonds

Answer 5

Sigma- direct overlap of orbitals
Pi- sideways overlap of p orbitals

Question 6

What reactions are alkanes involved in

Answer 6

Combustion
Halogenation

Question 7

How does branching affect the boiling point

Answer 7

Branching decreases alkanes boiling point
Less surface contact
Chains further apart
Strength of London forces decrease
Less energy req to overcome forces

Question 8

What is the general formula of alkanes

Answer 8

CnH2n+2

Question 9

Products formed in:
i) complete combustion
ii) incomplete combustion

Answer 9

i) Water + Carbon dioxide
ii) Water + Carbon monoxide

Question 10

How to test for alkanes

Answer 10

Add bromine water
If alkanes are present, solution goes from orange to colourless

Question 11

Potential dangers from CO

Answer 11

respiratory issues, dizziness, eventual death

Question 12

How do alkanes react with halogens

Answer 12

Free radical substitution

Question 13

Conditions for reaction with alkanes and halogens to occur

Answer 13

Uv light present

Question 14

3 steps involved for halogenation

Answer 14

Initiation
Propagation
Termination

Question 15

Which of these alkanes has the highest boiling point?
A Decane
B Hexane
C 2,3-dimethyloctane
D 2,3-dimethylbutane

Answer 15

A Decane

Question 16

Which equation represents a propagation step in the chlorination of methane?
A ●H + Cl2 → HCl + ●Cl
B ●Cl + CH4 → CH3Cl + ●H
C ●CH3 + Cl2 → CH3Cl + ●Cl
D ●CH3 + ●Cl → CH3Cl

Answer 16

C ●CH3 + Cl2 → CH3Cl + ●Cl

Question 17

5 marks
C2H6 + Cl2 C2H5Cl + HCl
State the conditions and outline a mechanism for this reaction. Show how butane can be formed in this reaction.

Answer 17

initiation
1: uv light/sunlight
2: Cl2 → 2Cl.;
propagation
3: C2H6 + Cl. → CH3CH2. + HCl;
termination
4: CH3CH2. + Cl2 → C2H5Cl + Cl.;
5: CH3CH2. + CH3CH2. → C4H10;

Question 18

The distillate is collected in the range 77–82 °C 0 7 .
1 Explain why the water should enter the condenser at the bottom and not at the top. [2 marks]

Answer 18

1. condenser fills with water
2. condenser is cool(er)