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AQA A-Level Chemistry > 3.3 Halogenoalkanes > Flashcards

3.3 Halogenoalkanes Flashcards

1
Q

General formula of halogenoalkanes

A

CₙH₂ₙX
(X = F,Cl, Br, I)

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2
Q

Functional group of halogeoalkanes

A

C-X

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3
Q

Why are halogenoalkanes more reactive than alkanes?

A

They have a polar bond

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4
Q

Uses of halogenoalkanes

A
  • Refrigerants
  • Solvents
  • Pharmaceuticals
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5
Q

What order are halogens named in a halogenoalkane

A

Alphabetical order

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6
Q

Nucleophile

A

An electron pair donator

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7
Q

Why do halogenoalkanes have nucleophilic substitution reactions?

A

They have a polar carbon-halogen bond

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8
Q

What happens in a nucleophilic substitution reaction?

A
  • Nucleophile donates electron pair to the δ+C atom
  • This forms a new colvalent bond
  • The C-X bond breaks
  • Halide ion is formed
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9
Q

Product of the reaction between halogenoalkanes and aqueous hydroxides

A

Alcohols

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10
Q

What type of reaction is halogenoalkane + aqueous hydroxide?

A

Hydrolysis (the mechanism is nucleophilic substitution)

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11
Q

Conditions for hydrolysis of halogenoalkanes with aqueous hydroxides

A
  • Warm
  • Aqueous
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12
Q

Reagent for hydrolysis of halogenoalkanes with aqueous hydroxides

A

NaOH / KOH

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13
Q

General equation for hydrolysis of halogenoalkanes

A

RX + NaOH → ROH + NaX
R - hydrocarbon chain
X - halogen

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14
Q

Ethanolic

A

Solution in ethanol

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15
Q

Product of the reaction between halogenoalkanes and potassium cyanide

A

Nitriles

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16
Q

Conditions for the reaction between halogenoalkanes and potassium cyanide

A
  • Warm
  • Ethanolic
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17
Q

Nitrile group

A

C≡N

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18
Q

General equation for the reaction between halogenoalkanes and potassium cyanide

A

RX + KCN → RCN + KX
R - hydrocarbon chain
X - halogen

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19
Q

What effect does reacting halogenoalkanes with cyanide have on the carbon chain?

A

Increases the chain length

20
Q

Mechanism for halogenoalkane + potassium cyanide

A

Nucleophilic substitution

21
Q

Mechanism for halogenoalkane + ammonia

A

Nucleophilic substitution

22
Q

Halogenoalkanes are reacted with ______ ammonia to form ______

A

Excess, amines

23
Q

Reagent for forming amines from halogenoalkanes

A

Excess ammonia

24
Q

Conditions for nucleophilic substitution of halogenoalkanes + ammonia

A
  • Warm
  • Sealed tube
  • Ethanolic
25
General equation for nucleophilic substitution of halogenoalkanes with ammonia
RX + **2**NH3 --> RNH2 + NH4 + X R - Carbon chain X - Halogen
26
What are the two roles of the ammonia molecules in nucleophilic substitution of halogenoalkanes
As a nucleophile and as a base
27
What determines the rate of substitution reactions in halogenoalkanes?
The carbon-halogen bond enthalpy
28
Which halogeneoalkanes have the fastest rate of hydrolysis?
Iodoalkanes C-I bonds have the lowest enthalpy so are the weakest and easiest to break
29
How can the rates of hydrolysis of halogenoalkanes be compaired?
- React chloro- bromo- and iodo-alkanes with aqueous silver nitrate - Ethanol as a cosolvent
30
Which variables need to be controlled when comparing the rates of hydrolysis in different halogenoalkanes?
- Equal number of moles of halogenoalkanes - Same chain length - Water bath to control temperature
31
Elimination
A reaction in which an atom or group of atoms is removed from a reactant.
32
Product of an elimination reaction with a halogenoalkane
An alkene
32
Reagent for elimination reactions with halogenoalkanes
NaOH / KOH
33
Conditions for elimination reactions with halogenoalkanes
- Ethanol as solvent - Reflux
34
Reflux
- A solution is heated to its boiling point - Gas produced enters a condenser and returns to the solution
35
Which atoms are removed in elimination of halogenoalkanes?
The halogen + a H from an adjacent C
36
Role of OH⁻ in elimination of halogenoalkanes
As a base
37
Ozone
O₃
38
How is ozone formed?
O₂ + O → O₃ In the upper atmosphere
39
Why is ozone beneficial?
It absorbs harmful UV radiation
40
CFCs
ChloroFluoroCarbons
41
How do CFCs cause the breakdown of ozone?
- They rise to the upper atmosphere - Break down to form chlorine radicals - Chlorine radicals catalyse the breakdown of ozone
42
Equations for the breakdown of ozone
Cl· + O₃ → O₂ + ClO· ClO· + O₃ → 2O₂ + Cl· Overall: 2O₃ → 3O₂
43
Alternative to CFCs
HFCs (Hydrofluorocarbons)
44
Uses of CFCs
Solvents and refrigerants
45
Properties of CFCs
- Non-toxic - Low reactivity
46
Why is an excess of ammonia used in nucleophilic substitution reactions?
To prevent further substitution reactions as the intermediate is a nucleophile

AQA A-Level Chemistry (15 decks)

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