4.2.2 haloalkanes

Question 1

what conditions are needed for nucleophilic substitution of haloalkanes

Answer 1

aqueous solution and reflux

Question 2

define hydrolysis

Answer 2

splitting of a molecule by a reaction with water

Question 3

what conditions are needed for hydrolysis of haloalkanes

Answer 3

reflux, addition of AgNO3

Question 4

why can flouroalkanes not undergo hydrolysis

Answer 4

the c-f bond is too strong

Question 5

give three properties of CFC’s

Answer 5

low reactivity, high volatility and non-toxicity

Question 6

give an alternative of CFC’s

Answer 6

HFC’s

Question 7

what is the ozone layer made of

Answer 7

naturally reoccurring O3 in the upper stratosphere that filters out much of the sun’s harmful UV radiation

Question 8

how is ozone formed

Answer 8

oxygen molecules decompose in UV light and then oxygen radicals react with oxygen molecules to form ozone

Question 9

when is the amount of ozone constant

Answer 9

• formation=depletion

* uv light absorbed=damaging uv rays

Question 10

what can increased UV on earth cause

Answer 10

skin cancer and crop mutation by preventing UV rays from penetrating Earth

Question 11

how do CFC’s catalyse ozone depletion

Answer 11

uv radiation caused c-cl bonds to break CFC molecules in the upper atmosphere and cl radicals are produced that catalyse the breakdown of ozone

Question 12

why are cfc’s still a concern

Answer 12

they have a long lifetime in the atmosphere and are released from disused items

Question 13

what are NO’s

Answer 13

a pollutant formed from thunderstorms and combustion engines

Question 14

how does NO break down ozone

Answer 14

acts as a catalyst to break down ozone

Question 15

what is the general equation for a reaction of alcohols to form a haloalkane

Answer 15

ROH + HX –> RX + H2O

Question 16

How can HBr and HI be made

Answer 16

-by adding H2SO4 to NaBr/NaI

eg NaBr + H2SO4 –> NaHSO4 + HBr

Question 17

what is the reagent when alcohols are substituted to make haloalkanes

Answer 17

sodium halide in sulfuric acid

Question 18

what is the general equation when alcohols are substituted to make haloalkanes

Answer 18

ROH + HX –> RX + H2O

Question 19

what type of mechanism is used when alcohols are substituted to make haloalkanes

Answer 19

electrophilic addition

Question 20

what is nucleophilic substitution in haloalkanes

Answer 20

when a nucleophile replaces a halogen atom for another atom or group of atoms

Question 21

what are the reagents when making alcohols from a haloalkane

Answer 21

potassium/sodium hydroxide

Question 22

what type of mechanism does making alcohols from a haloalkane use

Answer 22

nucleophilic substitution

Question 23

describe hydrolysis of haloalkanes

Answer 23

• water is a poor nucleophile and reacts slowly with haloalkanes so reflux is required
• aqueous silver nitrate is added
• halide ion will react with silver ions to form a precipitate

Question 24

what is the general equation for hydrolysis if haloalkanes

Answer 24

RX + H2O –> ROH + H-X

Question 25

state the reactivity of the halogens in hydrolysis and why

Answer 25

fastest
           I               
           Br
           Cl
slowest
the lower the bond enthalpy the weaker the bond, Cl has the strongest bonds and I has the weakest

Question 26

what are 2 alternative to CFC’s and why are they less damaging

Answer 26

• HFC’s can be used as they do not contain the C-Cl bond for example in refrigerators
• CO2 is used as a blowing agent for producing expanded polymers

Question 27

what were CFC’s used for and why

Answer 27

• used for aerosols, refrigerators and air-conditioning

- because they have low-reactivity, high volatility and non-toxicity