3.3 Halogenoalkanes

Question 1

What is the termination step in free radical substitution, use methane & chlorine as an example

Answer 1

Where two radicals react together

Question 2

Define a free radical

Answer 2

Species with an unpaired electron

Question 3

Write an equation for each of the following steps in the mechanism for the reaction of chloromethane with chlorine to form dichloromethane

Answer 3

Question 4

Haloalkanes produced from free radical substitution can react again with another halogen and undergo further substitution. How to prevent further substitution

Answer 4

Use excess alkane

Question 5

What are CFCs, state what they cause

Answer 5

Haloalkanes that contain both chlorine and fluorine
They cause depletion of ozone layer

Question 6

Write three equations to show how trichlorofluoromethane is involved in damaging the ozone layer

Answer 6

Question 7

Answer 7

Question 8

Why does fluoroethane not lead to the depletion of ozone

Answer 8

Doesn’t contain a chlorine
C-F bonds are strong and do not break

Question 9

Define a nucleophile

Answer 9

An electron-pair donor

Question 10

The different nucleophiles that react with haloalkanes in nucleophilic substitution

Answer 10

Question 11

Draw mechanism for nucleophilic substitution with NH3, CN and OH. Use bromoethane

Answer 11

Question 12

Reagent and conditions for nucleophilic substitution with OH^-

Answer 12

Reagent : NaOH or KOH
Conditions : aqueous solvent & warm

Question 13

Reagents and conditions for nucleophilic substitution by CN^-

Answer 13

Reagent : KCN
Conditions : water and ethanolic solvent

Question 14

Reagent and conditions for nucleophilic substitution by NH3

Answer 14

Reagents : Excess NH3
Conditions : Ethanol solvent, heat and pressure

Question 15

What is rate of a reaction equal to

Answer 15

1 / time

Question 16

Describe method for hydrolysis

Answer 16

Question 17

Reasons for different rates of hydrolysis

Answer 17

As bond enthalpy decreases, it is easier to break C - halogen bond
Weaker the bond, the faster the rate

Question 18

Name of mechanism from alkene to haloalkane
Reagents :
Conditions :

Answer 18

Electrophilic addition
Reagents : NaOH or KOH
conditions : hot & ethanolic solvent

Question 19

Outline mechanism,eliminations for 2-chlorobutane and draw all possible products

Answer 19

Question 20

State use of CFC’S

Answer 20

They are used as refrigerators

Question 21

Answer 21

D

Question 22

Question 23

Initiation step for CH3F in free radical substitution

Answer 23

F2 -> .2F

Question 24

Answer 24

Question 25

State conditions necessary for free radical substitution

Answer 25

UV light High temperature

Question 26

Linked to free radical substitution

Answer 26

C2H6 + 6Br2 -> C2Br6 + 6HBr

Question 27

State why ultraviolet light is needed in free radical substitution, use chlorine as an example

Answer 27

Provides enough energy to break covalent bonds in chlorine to form free radicals

Question 28

Answer 28

Question 29

Answer 29

Question 30

In ozone depletio, for formation of reactive species, what are you trying to form

Answer 30

A chlorine free radical

Question 31

Answer 31

B as it doesn’t contain chlorine

Question 32

Answer 32

Question 33

Answer 33

C-Br bond is weaker than C-Cl bond as C-Cl bond has higher bond enthalpy

Question 34

Explain how an atom can act as a catalyst

Answer 34

Not being used up in reaction Being unchanged at the end Is regenerated

Question 35

Chlorofluorocarbons are banned in many countries because of their effect on the environment. Why can a single radical cause the decomposition of many molecules in the ozone layer

Answer 35

Cl. (Radical) is regenerated and causes a chain reaction in the decomposition of ozone

Question 36

What does the dot represent in a radical atom

Answer 36

An unpaired electron

Question 37

Write an overall equation to represent the decomposition of ozone into oxygen

Answer 37

2O3 -> 3O2

Question 38

Answer 38

Question 39

State benefit to life on Earth of ozone in the upper atmosphere

Answer 39

Absorbs harmful UV radiation

Question 40

State how a CFC can contribute to global warming

Answer 40

Absorbs infrared radiation as molecule has polar bonds

Question 41

State how CFCs from chlorine atoms in the upper atmosphere

Answer 41

C- Cl bonds break

Question 42

Answer 42

Question 43

Define nucleophile

Answer 43

Electron pair donor

Question 44

Answer 44

Question 45

Answer 45

Electron pair donor

Question 46

CH3CH2Br reacts with NH3 to produce CH3CH2NH2, state why an excess of ammonia is needed in this reaction

Answer 46

To minimise further substitution as ethylamine can react further to form secondary amines

Question 47

Name compound CH3CH2CN

Answer 47

Propanenitrile

Question 48

Answer 48

Question 49

What compounds needed for nucleophilic substitution and which one usually involved in a bigger mark question as it has more steps

Answer 49

NH3 KCN KOH / NaOH NH3 has more steps than the others

Question 50

Answer 50

Sign is plus

Question 51

Skip part a)

Answer 51

Question 52

Answer 52

Question 53

Answer 53

Question 54

Answer 54

Question 55

Only do second part

Answer 55

Lower concentration Lower temperature Use water as an aqueous solvent

Question 56

Answer 56

Question 57

What type of stereoisomers are E- Z isomers

Answer 57

Geometrical isomers

Question 59

State reagent in elimination and it’s role in the mechanism

Answer 59

Reagent : NaOH / KOH Role : base

Question 60

Answer 60

Question 61

Answer 61

C because it is an alcohol

Question 62

For nucleophilic substitution, state the role of hydroxide ions is in the mechanism

Answer 62

Nucleophile / electron pair donor / lone pair donor

Question 63

Bromethane can undergo nucleophilic substitution, state the characteristic that enables it to undergo this reaction

Answer 63

There is a polar C-Br bind

Question 64

Conditions of elimination

Answer 64

- ethanolic solvent - concentrated hydroxide - high temperature

Question 65

If a warm dilute concentrated aqueous sodium hydroxide reacts with a haloalkane, what mechanism is this and what does it form

Answer 65

Nucleoliphilic substitution Alcohol

Question 66

Answer 66