CL 15- haloalkanes

Question 1

why do haloalkanes have higher boiling points than alkanes?

Answer 1

• contain london forces and permanent-permanent dipole forces which are stronger than just london forces in alkanes
• requires more energy to overcome (still have low boiling points)

Question 2

experiment to measure the rates of hydrolysis of haloalkanes

AgNO₃ and ethanol

Answer 2

1. set up 3 test tubes with 1cm³ of ethanol
2. add 2 drops of one of the haloalkanes to each test tube (R-Cl, R-Br, R-I)
3. warm to 60°C in water bath
4. warm 3 test tubes containing 1cm³ of AgNO₃
5. mix a silver nitrate and haloalkane test tube
6. time how long it takes for a precipitate to form

Question 3

why do we need ethanol in the experiment?

Answer 3

haloalkanes are insoluble, so using ethanol ensures that they dissolve and can react with the water molecules

Question 4

nucleophile

definition

Answer 4

electron pair donor

Question 5

explain the trend in the rates of hydrolysis of primary haloalkanes

in terms of carbon-halogen bonds

Answer 5

bond strength decreases
C-F > C-Cl > C-BR > C-I
the weaker the bond strength, the faster the hydrolysis

Question 6

when is ozone good?

Answer 6

when it’s in the stratosphere, prevents harmful UV light reaching organisms on earth

Question 7

when is ozone bad?

Answer 7

when it’s in the troposphere, harmful on respiratory tracts of animals

Question 8

what is ozone’s job?

think UV with lower wavelengths

Answer 8

entirely screen out 200-280nm wavelength UV-c
high energy so potentially very damaging
UV-a reaches earth’s surface and is responsible for skin aging
UV-b is partially filtered out by ozone and causes sunburn and cancer

Question 9

why is there a problem concerning ozone levels?

Answer 9

• the rate of removal of ozone used to equal the rate of production of ozone
• humans have added substances to the atmosphere that have disrupted the rate of removal

Question 10

uses of CFC’s

chlorofluorocarbon

Answer 10

• refrigerants, cools fridge down
• propellants (aerosol sprays)
• fire extinguishing (removed oxygen)

Question 11

equation for the production of halogen radicals (by the action of UV radiation on CFC’s in the upper atmosphere)

Answer 11

CF₂Cl₂ –> CF₂Cl. + Cl.

Question 12

the equation for the resulting catalysed breakdown of the earth’s protective ozone layer

Answer 12

O₃ + O –> 2O₂

Question 13

catalysed breakdowns of ozone by Cl.

propagation steps

Answer 13

Cl. + O₃ –> ClO. + O₂
ClO. + O –> Cl. + O₂

Question 14

catalysed breakdown of ozone by NO .

propagation steps

Answer 14

NO. + O₃ –> NO₂. + O₂
NO₂. + O –> NO. + O₂