Chapter 15 Key Concepts

Question 1

What affects the rate of hydrolysis

Answer 1

The strength of the CX bond. The strong the bond the slower the rate of hydrolysis

C-F is strongest
So fluoralkanes are unreactive so a large amount of energy needed to break the CF

C-I is weakest
So iodoalkanes react faster than bromoalkane which react faster than chloroalkanes

Question 2

How to measure the rate of hydrolysis of primary haloalkanes

Answer 2

Carry out the reaction in the presence of aq silver nitrate
As the reaction occurs X- made that reacts with Ag+ to make the AgX solid ppt

• water from the aq silver nitrate is the electrophile
• haloalkanes are insoluble in water so use an ETHANOL SOLVENT which allows the water and haloalkane to mix to make a single solution not two layers

Question 3

What are organohalogens and what are they used for

Answer 3

Molecules with at least one H atoms joined to a carbon chain
Rarely found it nature and not broken down in the environment
Uses
-general solvents CHCl3
-dry cleaning solvent C2H2Cl2 and C2HCl3
-making polymers C2H3Cl and C2F4
-flame Retardants CF3Br
-refrigerants F2CCl2 HCClF2 HCCl2F

Question 4

Dangers of UVB

Answer 4

Increased genetic damage
Increased risk on skin cancer in humans
Cataracts
Crop mutation

Question 5

Why were CFC and HCFC used and what were they used for?

Answer 5

Refrigerants
Aerosol propellants
Air conditioning units

CX bonds makes them very stable so stay in the troposphere for very long…until they reach the stratosphere where UV provides enough energy to break the CCl bond (because it has the lowest bond enthalpy) in photodissociation

Question 6

Major sources of NO radicals?

Answer 6

Lightning and aircraft travel in the stratosphere

Question 7

What was good about the whole CFC situation

Answer 7

Acceptance of scientific evidence explaining ozone depletion that led to government legislation against CFC use