haloalkanes

Question 1

Compare the reactivity of e.g. chloroalkane to bromoalkane in nucleophilic substitution

Answer 1

• Bromoalkane is more reactive than chloroalkane
• C-Br bond is weaker than C-Cl bond (C-X bond gets weaker down the group)
• Less energy is needed to break the C-Br bond

Question 2

define nucleophile

Answer 2

electron pair donor

Question 3

problem with combustion of polymers such as pvc

Answer 3

HCL toxic gas produced

Question 4

why is it important for the concentration of the ozone in the stratosphere maintained?

Answer 4

protects against UV radiation
which causes skin cancer cells

Question 5

suggest the formula of a compound that can be used as a refrigerant instead of CCl2F2

Answer 5

HFC
HCFC

Question 6

balanced equation for the depletion of the ozone

Answer 6

03 + 0 = 202

Question 7

role of Cl in depletion of the ozone

Answer 7

acts as a catalyst
gets used up then regenerated

Question 8

why is the C-halogen bond polar?

Answer 8

because halogen atom is more electronegative than carbon atom

Question 9

4 examples of nucleophiles

Answer 9

ammonia
water
hydroxide
cyanide

Question 10

define a hydrolysis

Answer 10

A chemical reaction involving water or an aqueous solution of a hydroxide ion, that causes the breaking of a bond

Question 11

reagents and conditions of nucleophillic substitution

Answer 11

R=NaOH(aq)
C=heat under reflux

Question 12

what does heating under reflux involve?
importance?

Answer 12

continuous boiling and condensing of a liquid
prevents loss of evaporation
not boiling dry

Question 13

what type of bond fission is nucleophillic substitution?

Answer 13

heterolytic

Question 14

what does a curly arrow show?

Answer 14

movement of an electron pair to make or break a covalent bond

Question 15

how is the rate of hydrolysis of primary alcohols meassured?

Answer 15

R= silver nitrate(aq) to test for halides
C=ethanol solvent and heat in a water bath

The ethanol (solvent) is needed to mix together the aqueous silver nitrate and the haloalkane

Question 16

method for rate of hydrolysis of primary alcohols

Answer 16

Incubate a set amount of haloalkane in a test tube in a water bath at 50oC​

Place a set amount of ethanol and aqueous silver nitrate in another test tube in a water bath at 50oC​

Mix the liquids together in one test tube and replace in the water bath at 50oC​

Measure the time taken for a precipitate to form​

Rate of hydrolysis reaction = 1 / time​

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Question 17

reagents and conditions of reaction of a haloalkane and a cyanide ion

Answer 17

R= NaCN or KCN
C=dissolved in ethanol

Question 18

why is the CN ion dissolved in water instead of ethanol?

Answer 18

water would react with the haloalkane in the hydrolysis reaction.​

Question 19

Why can ammonia behave as a nucleophile?

Answer 19

It has a lone pair of electrons which can be donated

Question 20

uses of halogen compounds

Answer 20

-polymers e.g. PVC, PTFE for non-stick pans
-as CFC chlorofluorocarbonsw

Question 21

why were CFCs used?

Answer 21

as inert, non-flammable and non-toxic

used as propellants, refrigerants and solvents for dry cleaning

Question 22

why are CFCs no longer used?

Answer 22

catalyse depletion of the ozone layer

Question 23

what replaced CFCs

Answer 23

HFCs hydrofluorocarbons

Question 24

what is the ozone layer?

Answer 24

Ozone, O3 , is in the stratosphere (upper atmosphere) and absorbs most of the Sun’s UV radiation.​

Question 25

What is the effect of the depletion of Ozone in the Ozone Layer?​

Answer 25

Ozone absorbs the Sun’s harmful UV radiation.​
If there is less ozone in the ozone layer, there is less protection against the UV radiation, causing a rise in skin cancer / eye cataracts.​

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Question 26

Explain why ozone depletion should be of major concern to humans.​

Answer 26

Ozone absorbs the Sun’s harmful UV radiation​
More UV radiation leads to a rise in skin cancer​