15.1 - 15.2

Question 1

What are halogenoalkanes

Answer 1

• alkanes with 1 or more halogen attached to it

Question 2

What do all haloalkanes have and why

Answer 2

• a polar bond as they have halogen attached to them

Question 3

What are haloalkanes attacked by

Answer 3

• nucleophiles

Question 4

Why do haloalkanes have polar bonds

Answer 4

• as halogens are more electronegative than carbon so they pull electrons towards themselves in a covalent bond

Question 5

What is a nucleophile

Answer 5

• a electron pair donor that forms a new covalent bond

Question 6

What are 4 examples of nucleophiles

Answer 6

1) NH3 (ammonia)
2) CN- (cyanide ions)
3) OH- (hydroxide ions)
4) H2O (water)

Question 7

What do curly arrows show

Answer 7

• the movement of electron pairs

Question 8

Where does the arrow start from and go to with nucleophiles

Answer 8

• starts from the lone pair on the nucleophile
• goes to the carbon atom

Question 9

What reaction do haloalkanes undergo

Answer 9

• nucleophilic substitution

Question 10

How do haloalkanes form alcohols

Answer 10

• nucleophilic substitution
  REAGENT: warm NaOH
• carried out under REFLUX

Question 11

In nucleophilic substitution the what type of bond fission happens when the bond between the carbon and the halogen break

Answer 11

• heterolytic bond fission as both electron move to form the bond to the halogen

Question 12

Is water a weak or strong nucleophile, and what affect does this have not he reaction

Answer 12

• weak so it is slower

Question 13

What is the reactivity of haloalkanes

Answer 13

• they become more reactive as we go down the group and hydrolysed (breaking the C-HALOGEN bond)the fastest

Question 14

What determines reactivity of haloalkanes

Answer 14

• bond strength
• bond enthalpy
  NOT THE BOND POLARITY

Question 15

How do we test for which haloalkane is which and what results should we get

Answer 15

1) Place chloroalkane, bromolakane and iodoalkane into 3 test tubes
2) add silver nitrate solution and ethanol (solvent) to each tube

RESULTS:
- iodoalkanes will form a yellow precipitate first as it has the weakest bond enthalpy so is more reactive
- bromoalkane will form a cream precipitate second
- chloroalkane will form a white precipitate last as it has the highest bond enthalpy and so is less reactive

Question 16

What are CFCs

Answer 16

• chlorofluorocarbons
• they have all their hydrogens replaces by chlorine and fluorine
• stable molecules but are broken down by UV)

Question 17

What do CFCs do

Answer 17

• break down ozone (O3) in the atmosphere

Question 18

How are the C-Cl bond in CFCs broken and what does it form

Answer 18

• by UV radiation in the atmosphere
• which forms radicals

Question 19

What catalyses the break down of ozone

Answer 19

• the radical formed when the C-Cl bonds are broken by UV radiation

Question 20

Why is a C-Cl bond more likely to be broken in CFCs compared to a C-F bond

Answer 20

• as C-Cl bonds have a lower bond enthalpy so not a lot of energy is needed to break the bond

Question 21

Write the free radical substitution reaction for CFCs

Answer 21

Initiation:
UV
CCl3F(g) ——> . CCl2F(g) + Cl .(g)

Propagation:
1) Cl .(g) + O3(g) —> O2(g) + ClO .(g)
2) ClO .(g) + O3(g) —> 2O2(g) + Cl .(g)

Termination:
Cl .(g) + Cl .(g) —> Cl2(g)

Question 22

What is the overall equation in the breakdown of the ozone and what is the catalyst

Answer 22

2O3(g) —> 3O2 (g)
* Cl . Is the catalyst

Question 23

What are other radicals that destroy ozone

Answer 23

• Nitrogen oxides

Question 24

True or false:
CFCs are now banned

Answer 24

• True

Question 25

Why do we need to ozone layer

Answer 25

• as it absorbs most harmful UV radiation that causes skin cancer

Question 26

What are alternative to CFCs

Answer 26

• HFCs (hydrofluorocarbon)=> beneficial as it doesn’t have the chlorine which would from radicals to break down the ozone layer

Question 27

How do we know that the alternative HFCs and other alternatives are working

Answer 27

• because the holes in the ozone layer are slowly becoming smaller