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A-Level OCR Chemistry > 15. Haloalkanes > Flashcards

15. Haloalkanes Flashcards

1
Q

What is an example of nucleophilic substitution of haloalkanes?

A

Hydrolysis

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2
Q

What happens during hydrolysis?

A

The halogen is replaced by an -OH group

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3
Q

What condition is required to start hydrolysis of haloalkane?

A

Heat under reflux

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4
Q

What solutions are used to measure the rate of hydrolysis of haloalkanes by water?

A
  1. aqueous silver nitrate (AgNO3)
  2. ethanol
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5
Q

What are the factors that affect the rate of hydrolysis? Which one is the main factor?

A

1. bond strength between carbon and halogen (outer shell)
2. polarity

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6
Q

What is the product when haloalkane is heated under reflux and reacts with sodium/potassium hydroxide (NaOH/KOH) ?

A

Alcohol

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7
Q

What is the product when haloalkane is heated under reflux and reacts with sodium/potassium cyanide (NaCN/KCN) in ethanol?

A

Nitrile

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8
Q

What is the product when haloalkane is heated under reflux and reacts with ammonia (NH3) in ethanol?

A

Amine

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9
Q

What does nucleophile mean?

A

An electron pair donor

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10
Q

What are the examples of nucleophiles?

A
  1. hydroxide ions (:OH-)
  2. water (H2O:)
  3. ammonia (:NH3)
  4. cyanide ions (:CN-)
  5. ethyl (CH2CH3)
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11
Q

Which carbon–halogen bond is the strongest? How is its rate of hydrolysis? Why?

A

C-Cl. It reacts the slowest because chlorine’s outer shell is the closest to the nucleus. This means that C-Cl bonds have the lowest bond enthalpy. Permanent dipole increases intermolecular forces, so the melting point is higher.

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12
Q

What conditions and solutions are required to produce alcohol when hydrolysing haloalkane?

A
  1. NaOH/KOH
  2. reflux
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13
Q

What conditions and solutions are required to produce nitrile when hydrolysing haloalkane?

A
  1. NaCN/KCN
  2. reflux
  3. ethanol
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14
Q

What conditions and solutions are required to produce amine when hydrolysing haloalkane?

A
  1. NH3
  2. reflux
  3. ethanol
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15
Q

What are organohalogen molecules?

A

Compounds that contain at least one halogen joined to a carbon.

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16
Q

What are organohalogen molecules used as?

A
  1. solvent
  2. making polymers
  3. dry cleaning agents
  4. flame retardants (阻燃劑)
  5. refrigerants
  6. pesticides
17
Q

Where is ozone layer found?

A

On the outer edge of the stratosphere

18
Q

How far is ozone above Earth’s surface?

A

Between 10 to 40 km

19
Q

What is the formula of ozone?

A

O3

20
Q

How does ozone form?

A

By a reaction involves O2 and an oxygen radical, which requires UV light. (O2 + O ⇌ O3)

21
Q

What does ozone do?

A

It absorbs most of the biologically damaging UV radiation from the sun called UV-B.

22
Q

What is the disadvantage of ozone?

A

It is corrosive

23
Q

What is CFC?

A

Chlorofluorocarbons

24
Q

What bonds do CFCs don’t have?

A

C-H bonds

25
Q

Why is CFC stable? What does it mean?

A

Because of the strength of its carbon-halogen bonds. This means that CFC has a long residence time (停留時間) in the troposphere.

26
Q

Until when CFC is not stable anymore?

A

Until they reach the stratosphere

27
Q

What does CFC do when it reaches the stratosphere? What does it mean to the ozone layer?

A

It starts to break down, forming a chlorine radical. It catalyses the breakdown of the Earth’s protective ozone layer.

28
Q

How do CFCs break down the ozone layer?

A

Once CFC is in stratosphere, UV radiation causes homolytic fission and breaks the carbon-halogen bond.

29
Q

Why does chlorine radical forms rather than other halogen radicals?

A

Because the C-Cl bond has the lowest bond enthalpy so it breaks the easiest. Once the C-Cl bond breaks, chlorine radical forms.

30
Q

How is ozone (O3) broken down?

A

The chlorine radical is very reactive and reacts with an ozone molecule, breaking down the ozone into oxygen.

31
Q

What is the initiation step of CF2Cl2?

A

CF2Cl2 > CF2Cl● + ●Cl

32
Q

What are the propagation steps of CF2Cl2?

A
  1. Cl● + O3 > ●ClO + O2 (ozone is broken down by the chlorine radical)
  2. ●ClO + O > Cl● + O2 (forms chlorine radical again, which breaks down more ozone)
33
Q

What is the overall equation of ozone being broken down?

A

O3 + O > 2O2

34
Q

What type of radical also breaks down ozone?

A

Nitrogen oxide radical (NO●)

35
Q

What is the propagation step of nitrogen oxide?

A
  1. NO● + O3 > NO2● + O2
  2. NO2● + O > NO● + O2

A-Level OCR Chemistry (10 decks)

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