Module 4 - Haloalkanes

Question 1

explain why haloalkanes are reactive

Answer 1

-they are electronegative
-a positive dipole forms on the C
-a negative dipole forms on the halogen as it is more electronegative
-the positive dipole carbon atom can be electron rich reagents (nucleophiles)

Question 2

define a nucleophile

Answer 2

-an electron pair donor

Question 3

describe nucleophilic substitution in the hydrolysis reaction of haloalkanes

Answer 3

1- nucleophiles (Nu-) attack the carbon of a carbon-halogen bond (C-X) as the electron pair on the nucleophile is attracted towards the small + charge on the carbon
2- the electrons in the C-X bond are repelled as the Nu- approaches the carbon atom
3- the Nu- bonds to the carbon and the C-X bond breaks, the two electrons move to the halogen, forming a halide ion

Question 4

explain the trend in reactivity of haloalkanes

Answer 4

-the strength of the bonds decreases down the group
-so the reactivity increases as the bond is longest and weakest so readily undergoes nucleophilic substitution

Question 5

define CFCs

Answer 5

-hydrocarbons that contain a C-Cl bond

Question 6

describe how CFCs destroyed the ozone layer

Answer 6

-the UV rays from the sun broke the C-Cl bond, producing free radicals
-this Cl free radical could then react with ozone (O3) in the atmosphere

Question 7

full equation for CFCs reacting with ozone

Answer 7

2O3 -> 3O2

Question 8

describe and explain how the effect of CFCs on the ozone layer was solved

Answer 8

-chemists produced HFC gases
-the C-F bond is stronger and not broken by UV rays
-so no free radicals produced

Question 9

name where CFCs were found

Answer 9

-aerosols
-cooling in fridges