haloalkanes

Question 1

explain why a carbon-halogen bond is polar (2)

Answer 1

halogen is more electronegative than carbon atom
the electron pair is attracted to the halogen atom

Question 2

what is the product of nucleophilic substitution with water

Answer 2

alcohol

Question 3

how to measure rate of hydrolysis with
chlorobutane
bromobutane
iodobutane

Answer 3

1. add 1cm3 of ethanol and 2 drops of each haloalkane to each test tube
2. place test tubes in water bath at 60degrees
3. add aqueous silver nitrate to a test tube and place in the water bath
4. when all tubes reach same temperature, add the aqueous AgNO3 to each test tube
5. time how long it takes for precipitate to form in each test tube

chloro- white
bromo- cream
iodo- yellow

Question 4

state the increasing rate of hydrolysis for
bromobutane
fluorobutane
iodobutane
chlorobutane

Answer 4

1. fluorobutane
2. chlorobutane
3. bromobutane
4. iodobutane

Question 5

why has fluorobutane got the slowest rate of hydrolysis

Answer 5

has the strongest C-F bond
greatest bond enthalpy
lots of energy needed to overcome

Question 6

why is it important that the test tubes are placed in the water bath at 60degrees at the same time

Answer 6

you are comparing rate so temperature must be constant
otherwise comparison is not fair as temperature would increase rate

Question 7

why are tertiary carbocations more stable than primary carbocations

Answer 7

alkyl groups reduce the charge on the carbocation by pushing electrons towards the positively charged ion, positive charge is reduced with more alkyl groups, so ion is more stable.
tertiary carbocation has 3 alkyl groups attached to the C, but primary carbocation only has 1 alkyl group attached.

Question 8

give the name of the mechanism of haloalkane to alcohol

Answer 8

nucleophilic substitution

Question 9

state and explain how rates of hydrolysis of chloroalkane and bromoalkane differ (2)

Answer 9

1. rate is slower with chloroalkane
2. C-Cl bond is stronger than C-Br bond

Question 10

what measurments and observation would allow the student to compare the rates of hydrlysis?

Answer 10

time taken for precipitates to appear

Question 11

iodopentane reacts faster than bromopentane, explain why (2)

Answer 11

1. C-I is weaker bond than C-Br
2. C-halogen bond breaks

Question 12

rate of hydrolysis depends on the halogen
state and explain how the halogen affects the rate of hydrolysis of the haloalkane (2)

Answer 12

1. weaker bond means faster reaction
2. C-I bond is weaker than C-F, C-I is hydrolysed the fastest, C-F is hydrolysed the slowest

Question 13

petanol can be prepared by hydrolysis of iodopentane

state the most appropriate technique that could be used to boil the reaction mixture for 20 minutes (1)

Answer 13

reflux