4.2.2 haloalkanes

Question 1

nucleophile

Answer 1

electron pair donator e.g. OH-, NH3,

Question 2

rate of substitution reactions

Answer 2

depends on strength of C - X bond

the weaker, the lower the bond enthalpy, the easier to break and the faster the reaction

Question 3

nucleophilic substitution with aqueous hydroxide ions

Answer 3

haloalkane > alcohol

reagent: potassium or sodium hydroxide

conditions: in aqueous solution, heat under reflux

Question 4

aqueous silver nitrate + haloalkane

Answer 4

halide combines with silver ion to form a silver halide precipitate

precipitate only forms when halide ion has left the haloalkane and so the rate of formation of precipitate can be used to compare reactivity of different haloalkanes

yellow - AgI
cream - AgBr
white - AgCl (s)

Question 5

chlorofluorocarbons (CFCs)

Answer 5

developed for use in aerosols, air conditioning etc

low reactivity, volatility and non-toxicity

detrimental effect on ozone layer

Question 6

ozone formation

Answer 6

Uv light causes O2 molecule to split to free radicals

O2 + UV > O + P

free radicals hit another O2 molecule, forming ozone

O + O2 > O3

filter out harmful UV and allow life to survive on earth
- UV light increases risk of skin cancer + crop mutation

Question 7

ozone depletion

Answer 7

O3 + UV light > O2 + O

rate of formation = rate of removal

Question 8

chlorine free radical effect on ozone

Answer 8

catalyse decomposition of ozone due to these reactions as they are regenerated (provide alternative route with lower activation energy)

Cl* + O3 > ClO* + O2

ClO* + O* > O2 + Cl*

overall:
O3 + O* > 2O2