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A Level Chemistry > Chapter 15 - Haloalkanes > Flashcards

Chapter 15 - Haloalkanes Flashcards

1
Q

What are haloalkanes?

A

Compounds containing hydrogen, carbon and at least one halogen atom

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2
Q

When two or more halogens are present in a haloalkane, how do you name it?

A

Put the two halogens in alphabetical order

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3
Q

How do you name haloalkanes?

A

Add the suitable prefix onto the name of the longest chain

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4
Q

What is a nucleophile?

A

An electron pair donor

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5
Q

Why are haloalkanes polar?

A

The carbon-halogen bond is polar. The halogen generally has a much higher electronegativity than carbon, so the electrons are pulled slightly towards the halogen and the carbon is left with a slight positive charge

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6
Q

Give three examples of nucleophiles

A

Hydroxide ions, :OH-
Water molecules, H2O:
Ammonia molecules, :NH3

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7
Q

What happens when a nucleophile is attracted to a carbon?

A

It donated electrons to form a new covalent bond

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8
Q

Why are nucleophiles attracted to carbon?

A

The carbon-halogen bond is polar, so carbon is left with a slight positive charge

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9
Q

What happens when a nucleophile reacts with a haloalkane?

A

The nucleophile replaces the halogen in a substitution reaction

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10
Q

What is nucleophilic substitution?

A

When a nucleophile replaces a halogen in a haloalkane

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11
Q

What happens when a haloalkane is hydrolysed?

A

An alcohol is formed

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12
Q

Describe the nucleophilic substitution reaction to make an alcohol from a haloalkane

A

1) The nucleophile (OH- in this case) approaches the slightly positively charged carbon
2) The direction of the attack of this nucleophile reduces the repulsion between the negatively charged hydrogen atom and the OH- ion
3) The lone pair of electrons on the nucleophile is donated to the carbon atom
4) A new bond forms between the carbon and the oxygen of the OH- ion
5) The carbon-halogen bond breaks by heterolytic fission
6) An alcohol and halide ion are formed

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13
Q

Why is the reaction different when water is used as a nucleophile?

A

It is much slower but will eventually get the same result

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14
Q

Which bond in the haloalkane is broken during hydrolysis?

A

The carbon-halogen bond

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15
Q

What does the rate of hydrolysis in haloalkanes rely upon?

A

The strength of the carbon-halogen bond

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16
Q

Which haloalkanes have the weakest bonds and so react fastest?

A

Iodoalkanes

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17
Q

Which haloalkanes have the strongest bonds and so react the slowest?

A

Fluoroalkanes

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18
Q

Will primary, secondary or tertiary haloalkanes react fastest?

A

Tertiary

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19
Q

Why do tertiary haloalkanes react fastest?

A

The tertiary haloalkane is much more stable than the primary one and reacts with a two-step mechanism

20
Q

What reaction would you conduct to measure the rate of hydrolysis of the haloalkanes?

A

1) Set up three test tubes, each containing 1cm^3 of ethanol and 2 drops of the haloalkane
2) Stand the tubes in a 60c water bath
3) Place a test tube containing 0.1 mol/dm3 silver nitrate in the same water bath, to allow everything to reach the same temperature
4) Add 1cm3 of the silver to each test tube
5) Start a timer and record your results

21
Q

What would you observe when you hydrolyse iodoalkanes?

A

A yellow precipitate forms rapidly

22
Q

What would you observe when you hydrolyse bromoalkanes?

A

A cream precipitate forms, more slowly than iodoalkanes but faster than chloroalkanes

23
Q

What would you observe when you hydrolyse chloroalkanes?

A

A white precipitate forms very slowly

24
Q

Why do we does the reaction between a haloalkane and silver nitrate produce a precipitate?

A

A halogen ion is formed, which forms bonds with the silver to produce silver halide, which is insoluble

25
Q

Why is ethanol used to assist the hydrolysis of haloalkanes?

A

It allows the water and haloalkane to mix to produce one single solution rather than two layers

26
Q

What did the Montreal Project aim to try and achieve?

A

Try and remove CFCs from the environment

27
Q

What are brominated flame retardants?

A

Compounds used by the electronics industry to reduce the flammability of products

28
Q

What are CFCs?

A

Haloalkanes

29
Q

What are organohalogens?

A

Compounds containing at least one hydrogen attached to the carbon chain

30
Q

Why are organohalogens bad?

A

They aren’t easily broken down

31
Q

Why is UV-B radiation bad?

A

It is commonly linked to sunburn

32
Q

Why is it bad that the ozone layer is being depleted?

A

More UV-B rays can reach earth, leading to an increase in genetic mutations and skin cancer

33
Q

What does the ozone layer do?

A

Absorbs harmful UV-B rays from the sun to stop them coming to earth

34
Q

Chemical formula for ozone

A

O3

35
Q

How is ozone made?

A

Very high levels of Uv radiation breaks an oxygen molecule into two oxygen radicals
An equilibrium then forms between oxygen (O2) and oxygen radicals making ozone and ozone breaking down to produce the reactants

36
Q

Why are CFCs very stable?

A

They have very strong bonds

37
Q

Why are CFCs bad?

A

They are generally very stable until they reach the stratosphere. Here, they break down, releasing chlorine radicals that start to break down the ozone and upset the equilibrium

38
Q

How does the carbon-halogen bond in CFCs break?

A

Sufficient energy is provided by UV radiation, which makes the bond break by homolytic fission, forming radicals

39
Q

What is the equation for the photodissociation of CF2Cl2 to form chlorine radicals?

A

CF2Cl2 -> CF2Cl. + .Cl

40
Q

What does chlorine actually do to ozone?

A

Once chlorine radicals are formed, they react with ozone to form an intermediary (ClO.) and an oxygen molecule. The ClO. then reacts with an oxygen atom to form Cl. + O2. Chlorine destroys the ozone and turns it into oxygen

41
Q

How is nitrogen oxide?

A

Aircraft engines and lightning

42
Q

Equations for nitrogen oxide breaking down O3

A

NO. + O3 -> NO2. + O

NO2. + O -> NO. + O2

43
Q

How do nitrogen oxide and chlorine radicals affect the breakdown of ozone?

A

They catalyse it

44
Q

Name three compounds that are currently being used as alternatives to CFCs

A

HCFCs, hydrocarbons and HFCs

45
Q

Why are HFCs good?

A

They contain no chlorine so don’t break down the ozone

46
Q

Why are HCFCs and HFCs bad?

A

They’re greenhouse gases and much worse than carbon dioxide

A Level Chemistry (29 decks)

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