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Completed AQA A level Chemistry > 3.3 Halogenoalkanes > Flashcards

3.3 Halogenoalkanes Flashcards

1
Q

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

A

Where two radicals react together

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2
Q

Define a free radical

A

Species with an unpaired electron

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3
Q

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

A
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4
Q

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

A

Use excess alkane

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5
Q

What are CFCs, state what they cause

A

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

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6
Q

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

A
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7
Q
A
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8
Q

Why does fluoroethane not lead to the depletion of ozone

A

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

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9
Q

Define a nucleophile

A

An electron-pair donor

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10
Q

The different nucleophiles that react with haloalkanes in nucleophilic substitution

A
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11
Q

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

A
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12
Q

Reagent and conditions for nucleophilic substitution with OH^-

A

Reagent : NaOH or KOH
Conditions : aqueous solvent

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13
Q

Reagents and conditions for nucleophilic substitution by CN^-

A

Reagent : KCN
Conditions : water and ethanolic solvent

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14
Q

Reagent and conditions for nucleophilic substitution by NH3

A

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

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15
Q

What is rate of a reaction equal to

A

1 / time

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16
Q

Describe method for hydrolysis

A
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17
Q

Reasons for different rates of hydrolysis

A

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

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18
Q

Name of mechanism from haloalkane to alkene
Reagents :
Conditions :

A

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

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19
Q

Outline eliminations for 2-chlorobutane and draw all possible products

A
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20
Q

State use of CFC’S

A

They are used as refrigerators

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21
Q
A

D

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22
Q
A
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23
Q

Initiation step for CH3F in free radical substitution

A

F2 -> .2F

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24
Q
A
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25
Q

State conditions necessary for free radical substitution

A

UV light
High temperature

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26
Q

Linked to free radical substitution

A

C2H6 + 6Br2 -> C2Br6 + 6HBr

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28
Q

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

A

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

31
Q

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

A

A chlorine free radical

32
Q
A

B as it doesn’t contain chlorine

34
Q
A

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

35
Q

Explain how an atom can act as a catalyst

A

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

36
Q

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

A

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

37
Q

What does the dot represent in a radical atom

A

An unpaired electron

38
Q

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

A

2O3 -> 3O2

40
Q

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

A

Absorbs harmful UV radiation

41
Q

State how a CFC can contribute to global warming

A

Absorbs infrared radiation as molecule has polar bonds

42
Q

State how CFCs from chlorine atoms in the upper atmosphere

A

C- Cl bonds break

44
Q

Define nucleophile

A

Electron pair donor

46
Q
A

Electron pair donor

47
Q

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

A

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

48
Q

Name compound CH3CH2CN

A

Propanenitrile

50
Q

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

A

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

51
Q
A

Sign is plus

52
Q

Skip part a)

56
Q

Only do second part

A

Lower concentration
Lower temperature
Use water as an aqueous solvent

58
Q

What type of stereoisomers are E- Z isomers

A

Geometrical isomers

60
Q

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

A

Reagent : NaOH / KOH
Role : base

62
Q
A

C because it is an alcohol

63
Q

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

A

Nucleophile / electron pair donor / lone pair donor

64
Q

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

A

There is a polar C-Br bind

65
Q

Conditions of elimination

A
  • ethanolic solvent
  • concentrated hydroxide
  • high temperature
66
Q

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

A

Nucleoliphilic substitution
Alcohol

Completed AQA A level Chemistry (2 decks)

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