Haloalkanes

Question 1

Name a use of haloalkanes

Answer 1

They’ve been used to make plastics like PVCs + PTEEs and as refrigerators and fire extinguishers (because they are non-toxic and non-flammable)

Question 2

Why are CFCs good solvents and refrigerants?

Answer 2

Because they are non-toxic and low in reactivity

Question 3

What is ozone and where does it exist?

Answer 3

Ozone is an allotrope of oxygen - O3 and exists as a layer in the upper atmosphere

Question 4

What is beneficial about ozone

Answer 4

Its absorbs UV radiation from sunlight protecting humans and the environment from damaging UV rays

Question 5

When is ozone formed?

Answer 5

Formed when UV light breaks down O2 molecules into radicals which react with more oxygen to form ozone

Question 6

What is the equation for ozone formation?

Answer 6

O2 -> 2O•
O2 + O• -> O3
Overall: 3O2 -> 2O3

Question 7

In 1970s what was discovered about the ozone layer of Antarctica and why did this happen.

Answer 7

in 1970s research discovered the ozone layer over Antarctica as considerably thinner than expected due to the reaction of chlorine radicals with ozone produced by the break down of CFC’s

Question 8

Name the effects of Ozone depletion

Answer 8

Skin ailments, disturbed plant lifecycles, destruction of marine life

Question 9

What are the causes of ozone depletion?

Answer 9

CFCs being released into the atmosphere

in the upper atmosphere uv light causes the C-CL bond present in CFC’s to break forming Cl radicals

Question 10

What is the role of the Cl radical in ozone depletion?

Answer 10

The Cl radical then catalyses the decomposition of Ozone resulting in a hole in the ozone layer

Question 11

What the equation for ozone depletion?

Answer 11

Cl• + O3 -> ClO• + O2
ClO• + O3 -> Cl• + 2O2
Overall: 2O3 -> 3O2

Question 12

Why is Cl• a catalyst?

Answer 12

Because they are used and reformed

Question 13

What did the Montreal Protocol do?

Answer 13

Banned the use of CFCs

Question 14

Why did HFCs replace CFCs

Answer 14

The CF bond is stronger than the CCl

bond, these molecules are less likely to be broken down by uv radiation

Question 15

What happens when haloalkanes react?

Answer 15

The C-Hal bond breaks

Question 16

How readily the bonds break down depend on what?

Answer 16

Bond enthalpy and bond polarity

Question 17

Halogen is more electronegative than the
Carbon so the bond will be_______
This means the C atom is slightly _________ charged (electron deficient) and is readily attacked by a __________
The electronegativity of group 7 _________ as you go down the group
So the halogenoalkane with the most polar bond is ________
C- F reactivity __________ down group 7

Answer 17

Polar
Positively 
Nucleophile
Decreases
Fluorine
Decreases

Question 18

When electronegativity increases reactivity ___________

Answer 18

Decreases

Question 19

bond enthalpy __________ as you go down group 7
Fluorine is the smallest halogen so the shared pair of electrons are very _________ attracted to the nucleus
This makes the bond strong so ____ energy is needed to break the bond. This implies that the reactivity would ________ as you go down group 7

Answer 19

Decreases
Strongly
More
Increase

Question 20

How can reactivity be determined experimentally?

Answer 20

Reactivity is determined experimentally by using equal volumes of each haloalkane + heating them with aqueous silver nitrate at 60°

Question 21

Name the precipitates formed for chloro,bromo,iodo butane and time taken to appear

Answer 21

1-chlorobutane - white precipitate - 720s to appear
1- bromobutane - cream precipitate - 12s to appear
1-iodobutane - yellow precipitate - 3s to appear

Question 22

Reactivity _________ down group 7 so bond enthalpy is ______ important than bond polarity

Answer 22

Increases

More

Question 23

_____ polar bonds -> more readily attracted by _________ ( C atom is electron ________)

Answer 23

more
nucleophile
deficient

Question 24

Whats a nucleophile

Answer 24

Electron pair donors

Question 25

What is the job of nucleophiles

Answer 25

attack and form bonds with positively charged carbon atoms

donate their lone pair of electrons to an electron deficient atom to form a dative covalent bond

Question 26

Define substitution

Answer 26

Replacement of an atom or group of atoms with another atom or group of atom