haloalkanes [O1] PAPER 2

Question 1

[X=halogen]

reaction between a haloalkane and NaOH to form an alcohol and NaX

1. conditions?
2. mechanism?
3. what is the role of NaOH?

Answer 1

1. warm, aqueous
2. nucleophilic substitution
3. nucleophile

Question 2

[X=halogen]

reaction between a haloalkane and KCN to form a cyanide and KX

1. conditions?
2. mechanism?
3. what is the role of CN?

Answer 2

1. warm, ethanolic, aqueous
2. nucleophilic substitution
3. nucleophile

Question 3

[X=halogen]

reaction between a haloalkane and ammonia to form an amine

1. conditions?
2. mechanism?
3. what is the role of NH3?

Answer 3

1. excess concentrated ethanolic NH3
2. nucleophilic substitution
3. nucleophile

Question 4

[X=halogen]

reaction between a haloalkane and KOH to form an alkene, water and KX

1. conditions?
2. mechanism?
3. role of OH ions?

Answer 4

1. hot, ethanolic
2. elimination
3. base

Question 5

what is a nucleophile?

Answer 5

electron pair donor

Question 6

what are the three steps of free-radical substitution?

Answer 6

1. initiation
   (molecule -> radical + radical)
2. propagation
   (molecule + radical -> radical + molecule)
3. termination
   (radical + radical -> molecule)

Question 7

what conditions are required for free-radical substitution and why?

Answer 7

• UV light
• break (C-X, C-H) bonds

[X=halogen]

Question 8

what is (1) the overall equation for the formation of chloromethane from methane and (2) the mechanism?

Answer 8

(1) CH4 + Cl2 -> CH3Cl + HCl
[for balancing - number of substitutions = number in front of HCl and Cl2]

(2) free-radical substitution

Question 9

write an equation to represent the overall decomposition of ozone into oxygen

Answer 9

2O3 -> 3O2

Question 10

what is the species responsible for the catalytic decomposition of ozone in the upper atmosphere?

Answer 10

Cl• (chlorine free-radical)

Question 11

write two equations that show how chlorine atoms (Cl•) act as a catalyst in the decomposition of ozone and explain how these reactions show that Cl• is a catalyst

Answer 11

Cl• is unchanged at the end

Question 12

during an experiment carried out within a lab, why are small amounts of the reactants used for the experiment, considering sulfur dioxide is one of the products

Answer 12

sulfur dioxide is toxic

Question 13

why would a molecule with C–Br bonds react faster than a molecule with C–Cl bonds in the same conditions?

Answer 13

C–Br is weaker than C–Cl

(as Cl is more electronegative)

Question 14

Explain why a single chlorine radical can cause the decomposition of many molecules of ozone.

Answer 14

Cl• is regenerated and causes a chain reaction in the decomposition of ozone

Question 15

Give one reason why bonds in molecules such as carbon dioxide and 1,1,1-trifluoroethane absorb infrared radiation.

Answer 15

because the bonds vibrate

OR

because the bonds are polar

Question 16

Explain why the halogenoalkane is attacked by the nucleophile in a nucleophilic substitution reaction.

Answer 16

[X = halogen]
• X is more electronegative than carbon
• Carbon is partially positive
• Lone electron pair on the nucleophile is donated to the partially positive carbon

Question 17

State why the ozone layer is beneficial for living organisms.

Answer 17

absorbs harmful uv

Question 18

State how chlorofluorocarbons (CFCs) form chlorine atoms in the upper atmosphere.

Answer 18

C–Cl bonds break