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AQA A-Level Chemistry > Halogenalkanes > Flashcards

Halogenalkanes Flashcards

1
Q

What are the two types of reactions that can occur with haloalkanes?

A

Only elimination or substitution reactions can occur

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2
Q

Describe and explain the nucleophilic substitution of bromoethane with aqueous hydroxide ions to produce ethanol

A
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3
Q

Describe and explain the nucleophilic substitution of bromoethane with cyanide ions to produce propanenitrile

A
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4
Q

Describe and explain the nucleophilic substitution of bromoethane with ammonia to produce a primary amine

A
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5
Q

State what is meant by the term nucleophile

A

An electron pair donater.

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6
Q

What is hydrolysis?

A

Splitting molecules using water

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7
Q

How can we test for halogenoalkanes? (brief)

A

Do a substitution reaction which turns the halogen into a halide ion
Then test for that ion with silver nitrate soln.

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8
Q

Describe how you would test for haloalkanes

A

Warm the haloalkane with NaOH soln. in a mix of ethanol and H2O
Halogen displaced to become an ion
Acidify with dilute nitric acid and then add silver nitrate
Various precipitates may be formed
You can confirm the precipitate by adding ammonia soln.

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9
Q

Why do you acidify the halide ion mixture with nitric acid?

A

To prevent any unreacted OH- ions reacting with the silver and giving a confusing precipitate

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10
Q

Adding silver nitrate soln. to a halide ion produces a white precipitate. What ion is it?

A

Cl-

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11
Q

Adding silver nitrate soln. to a halide ion produces a very pale yellow precipitate. What ion is it?

A

I-

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12
Q

Adding silver nitrate soln. to a halide ion produces a very pale cream precipitate. What ion is it?

A

Br-

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13
Q

What are the conditions for haloalkane substitution by OH- ions?

A

Aqueous and warm

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14
Q

What are the conditions for haloalkane substitutions by CN- ions?

A

Aqueous/alcohol
Warm

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15
Q

What is produced by haloalkane substitution with CN- ions?

A

A nitrile

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16
Q

What are the conditions for haloalkane substitution by NH3?

A

Excess ammonia (NH3)
Sealed tube

17
Q

Give a general reaction for the substitution of a haloalkane by NH3

A

R-X + 2NH3 –> R-NH2 = NH4+X-

18
Q

In substitution by NH3, NH3 acts in two ways. What are they?

A

As a nucleophile and as a base

19
Q

What are the reagents and conditions for elimination reactions?

A

Reagents - NaOH/KOH
Conditions - dissolved in ethanol

20
Q

Describe and explain the elimination reaction of 2-bromopropane with ethanolic hydroxide ions to form propene

A
21
Q

What does CFC stand for?

A

Chlorofluorocarbons

22
Q

What are the common uses of CFCs and why?

A

Low toxicity, low reactivity and low flammability led to common use as refrigerants and aerosol propellants

23
Q

What is the ozone layer?

A

A thin layer of the atmosphere consisting of O3, that filters out some UV

24
Q

What does the ozone layer do?

A

Filter out shorter wavelengths of UV light that would be harmful to most life in larger doses

25
Q

Why do HCFCs not affect the ozone layer?

A

They don’t have the C-Cl bond

26
Q

What is an ozone molecule?

A

O3

27
Q

CFCs affect the ozone layer. Name the reaction that occurs

A

Free radical substitution

28
Q

Give an overall balanced formulaic equation for the free radical substitution of ozone

A

2O3 –> 3O2

29
Q

Why are CFCs such a problem?

A

Attack ozone
Cl* regenerated so can affect others
CFCs have long lifetime (20-100yrs)

30
Q

Explain why an excess of ammonia is needed in the substitution of NH3 to produce a high yield of amine

A

NH3 has two roles - firstly as a nucleophile and secondly as a base

31
Q

What is the role of Cl in the decomposition of ozone?

A

Acts as a catalyst

32
Q

What is the suffix of a nitrile?

A

-anenitrile

33
Q

CFCs affect the ozone layer. Describe the reaction that occurs

A

UV light breaks C-Cl bond –> CF3 + Cl
Cl radicals attack ozone –> regenerate more Cls
Cl + O3 –> ClO* + O2
ClO* + O3 –> Cl* + 2O2
Cl* + Cl* –> Cl2

34
Q

Describe and explain the free radical mechanism of ethane with bromine

A

AQA A-Level Chemistry (36 decks)

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