Haloalkanes

Question 1

What is a haloalkane?

Answer 1

A compound in which a halogen atom has replaced at least one of the hydrogen atoms in an alkane chain.

Question 2

Is a carbon-halogen bond polar or non polar and why?

Answer 2

Polar, because the halogen atom is more electronegative than carbon.

Question 3

What species does the electron deficient C atom attract?

Answer 3

Nucleophiles.

Question 4

What is a nucleophile?

Answer 4

An electron pair donor.

Question 5

What are examples of nucleophiles?

Answer 5

OH-
NH3
H2O
CN-

Question 6

What is nucleophilic substitution?

Answer 6

An electron pair donor replaces a halogen atom.

Question 7

What is hydrolysis?

Answer 7

A chemical reaction involving water/an aqueous solution of a hydroxide ion that causes the breaking of a bond in a molecule.

Question 8

What reagents/conditions/products are required for nucleophilic substitution of a haloalkane and hydroxide ions?

Answer 8

• aqueous alkali e.g., NaOH
• heat under reflux
• forms an alcohol and a halogen ion

Question 9

What does heating under reflux involve?

Answer 9

The continuous boiling and condensing of a liquid, allowing prolonged heating and preventing loss by evaporation.

Question 10

What does the reactivity of a haloalkane depend on?

Answer 10

The strength of the carbon-halogen bond which breaks during the reaction by heterolytic fission.

Question 11

State the order of reactivity of haloalkanes.

Answer 11

MOST REACTIVE/WEAKEST BOND
- C-I
- C-Br
- C-Cl
- C-F
LEAST REACTIVE/STRONGEST BOND

Question 12

What reagents/conditions/products are present in measuring the rate of hydrolysis of primary haloalkanes?

Answer 12

• aqueous silver nitrate, AgNO3(aq)
• ethanol solvent and heat(water bath)
• alcohol and silver halide

Question 13

How do you calculate the rate of hydrolysis?

Answer 13

1/time.

Question 14

What are the results of the rate of hydrolysis with Cl, Br and I?

Answer 14

Cl- white precipitate, most time, slowest rate
Br- cream precipitate
I- yellow precipitate, least time, fastest rate

Question 15

Why is the rate of hydrolysis of 1-iodobutane faster than the rate of hydrolysis of 1-chlorobutane?

Answer 15

-the rate of hydrolysis depends upon the strength of the Carbon-Halogen bond
-the C-I bond is weaker than the C-Cl bond
-less energy is needed to break the C-I bond so the rate of hydrolysis is faster

Question 16

What are CFCs?

Answer 16

Chloro Flouro Carbons.

Question 17

What were the uses of CFCs?

Answer 17

Refrigerants, aerosol propellants.

Question 18

Why are CFCs no longer used?

Answer 18

Their use results in the depletion of the ozone layer.

Question 19

What has replaced CFCs?

Answer 19

HFCs (hydroflourocarbon) and HCFCs (hydrochloroflourocarbons).

Question 20

What is the ozone layer?

Answer 20

A region of the Earth’s stratosphere that absorbs the Sun’s harmful UV radiation. It contains high concentrations of ozone(O3).

Question 21

What does UV initially break oxygen molecules into?

Answer 21

Oxygen radicals
O2→2O.

Question 22

What has happened to the ozone layer?

Answer 22

The use of CFCs has increased the rate of ozone depletion causing a ‘hole’ in the ozone layer.

Question 22

Show the equation for the equilibrium involving O2 and oxygen radicals. What does the equation represent?

Answer 22

O2 + O⇌O3
The rate of ozone formation is equal to the rate of ozone depletion.

Question 23

What is the effect of the depletion of ozone in the ozone layer?

Answer 23

Less protection against the Sun’s UV radiation so a rise in skin cancer.

Question 24

How have CFCs caused the breakdown of ozone?

Answer 24

CFC molecules produce Cl. radicals in the stratosphere by homolytic fission of a C-Cl bond. The processes of radical substitution.