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Chemistry Module 4 > 4.2.2 Haloalkanes > Flashcards

4.2.2 Haloalkanes Flashcards

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1
Q

Classifying haloalkanes

A

Primary
Secondary
Tertiary

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2
Q

Primary haloalkanes

A

One carbon attached to carbon atom adjoining the halogen

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3
Q

Secondary haloalkane

A

Two carbons attached to the carbon atom adjoining the halogen

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4
Q

Tertiary haloalkane

A

Three carbons attached to the carbon atom adjoining the halogen

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5
Q

Nucleophile

A

Electron pair donator

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6
Q

Substitution

A

Swapping a halogen atom for another atom or group of atoms

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7
Q

What do nucleophiles always have

A

Lone pair

So they can donate the electrons

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8
Q

Mechanism of nucelophilic substitution

A

Nucleophile attacks carbocation (has slight positive change as electro negativity difference between carbon and halogen)
Curly arrow from lone pair of electrons to carbocation then centre of the bond

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9
Q

What do the rate of substitution reactions depend on

A

Strength of carbon-halogen bond

Weaker bond the easier to break the faster the reaction

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10
Q

Speed of nucleophilic substitution

A

C-I
C-Br
C-Cl
C-F

Iodo is fastest and fluoro is slowest as strength of C-F is such that fluoro is unreactive

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11
Q

Nucleophilic substitution with aqueous hydroxide ions

A 
Haloalkane->alcohol 
Reagent: potassium or sodium hydroxide 
Conditions: in aqueous solution, heat under reflux 
Mechanism: nucleophilic substitution 
Type of reagent: nucleophile, OH-
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12
Q

Why is it important that ions will be aqueous

A

If the solvent is changed to ethanol an elimination reaction occurs

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13
Q

What is hydrolysis

A

Splitting of a molecule by a reaction with water

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14
Q

Water as a nucleophile

A

Poor as it reacts slowly with haloalkanes in a substitution reaction
Use reflux or heat for more than 20 minutes

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15
Q

adding aqueous silver nitrate

A

halide group leaving combines with a silver ion to form silver halide precipitate
this can be used to determine the reactivity of the halides
faster ppt formed, faster substitution reaction, more reactive the halide

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16
Q

reactivity fastest to slowest halogens

A

iodine
bromine
chlorine

17
Q

colour ppt formed by halides

A

iodine- yellow
bromine-cream
chlorine- white

18
Q

equation showing reaction between haloalkane and silver nitrate

A

CH3CH2I + H2O -> CH3CH2OH + I- + H+

Ag+ (aq) + I- (aq) -> AgI (s) yellow ppt

19
Q

what is a CFC

A

chlorofluorocarbon

20
Q

original reason for development of CFC’s

A

aerosols
refrigerants
air-conditioning

due to their low reactivity, volatility and non-toxicity

21
Q

why have lots of CFC’s been banned

A

due to toxicity of haloalkanes and detrimental effect on ozone layer in atmosphere

22
Q

what are now used instead of CFC’s and why

A

HFC’s (hydro fluoro carbons)

much safer as they don’t contain the C-Cl bond

23
Q

why is the natural ozone layer beneficial

A

O3

filters out most of the sun’s harmful UV radiation

24
Q

ozone in the lower atmosphere

A

pollutant

contributes to formation of smog

25
Q

how is ozone continually being formed and broken down

A

in the stratosphere

by action of ultraviolet radiation

26
Q

reaction for formation of ozone

A

O + O2 (reversible) O3

27
Q

ozone depletion and reaction

A

reverse of the formation reaction
energy is supplied by ultraviolet light

O3+ uv light -> O2 + O

28
Q

ozone formation

A

uv light causes an oxygen molecule to split into free radicals
O2 + UV light -> O. + O.

then free radical hits another O2 molecule ozone forms
O. + O2. -> O3

29
Q

what does rate of ozone formation equal

A

rate of ozone depletion

30
Q

what may catalyse the breakdown of ozone

A

radicals from CFC’s

nitrous oxides from thunderstorms or aircrafts

31
Q

how are chlorine radicals formed in the upper atmosphere

A

when energy from ultra-violet radiation causes C-Cl bonds in CFC’s to break

32
Q

chlorine free radicals and ozone explanation

A

free radicals catalyse the decomposition of ozone because they are regenerated
provide an alternative route with lower activation energy
contribute to the formation of a hole in the ozone layer

33
Q

equation of ozone decomposition with chlorine

A

Cl. + O3 -> ClO. + O2
ClO. + O. -> O2 +Cl.

overall: O3 + O. -> 2 O2

the chlorine free radical is regenerated so can destroy thousands of ozone molecules

34
Q

ozone decomposition including nitrous oxides

A

NO + O3 -> NO2 + O2
NO2 + O. -> O2 + NO

overall: O3 + O. -> 2 O2

35
Q

remaining concern of CFC’s

A

still entering the atmosphere from disused items and still used for some purposes in certain countries
long lifetime in the atmosphere and takes a long time for CFC’s to reach the upper atmosphere

Chemistry Module 4 (8 decks)

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