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AS Chemistry > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

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1
Q

What is the general formula of the homologous series of halogenoalkanes?

A

CnH2n+1X

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2
Q

Why is the C-X bond polar?

A

Bc the halogen atom is more electronegative than the C atom

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3
Q

Why do C-X bonds become less polar as you go down the group?

A

Halogens become less electronegative as you go down the group

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4
Q

What intermolecular forces are present in halogenoalkanes?

A

van der Waals forces and permanent dipole dipole interactions

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5
Q

Why does boiling point increase as chain length of the halogenoalkanes increase?

A

Greater Mr so greater van der Waals forces between the molecules

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6
Q

Why does the boiling point increase as the halogen used goes down the group?

A

Greater Mr so greater van der Waals forces between the molecules

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7
Q

Are halogenoalkanes soluble in water?

A

No

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8
Q

What are halogenoalkanes soluble in?

A

Organic solvents

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9
Q

Why is free radical substitution a photochemical reaction?

A

Bc it’s brought about by light

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10
Q

What is a free radical?

A

An atom or a group with an unpaired electron

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11
Q

What is homolytic fission?

A

When a bond breaks equally

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12
Q

Why is free radical substitution a chain reaction?

A

For every reactive species you start off with, a new one is generated

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13
Q

What does free radical substitution do?

A

Forms halogenoalkanes

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14
Q

Explain the process of free radical substitution

A

Initiation - free radicals made by homolytic fission caused by UV light
Propagation - free radicals act as catalyst to form halogenoalkanes
Termination - the chain reaction is terminated bc free radicals come together to make non-free radicals

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15
Q

What is ozone?

A

It’s an allotrope of oxygen found in the ozone layer of the stratosphere

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16
Q

Why is ozone useful?

A

Absorbs UV light from the Sun

17
Q

Why is UV light dangerous?

A

Can cause sunburn, cataracts in the eye, skin cancer, damage to plant tissue and reduce plankton populations in the ocean

18
Q

Why is ozone depleting?

A

Halogen free radicals such as CFCs

19
Q

What are CFCs used in?

A

Aerosols, solvents, coolants in refrigerators bc non-toxic and non-flammable

20
Q

Why are CFCs dangerous?

A

Released into the lower atmosphere where they do not degrade they diffuse into the stratosphere where they’re made into free radicals and then cause ozone to deplete

21
Q

What solutions have governments made to stop ozone depletion?

A

200 countries have signed the Montreal Protocol which pledges to wipe out ozone-depleting agents
Chlorine-free compounds being used like hydrofluorocarbons

22
Q

What are primary halogenoalkanes?

A

2 hydrogens attached to the carbon with the halogen

23
Q

What are secondary halogenoalkanes?

A

1 hydrogen attached to the carbon with the halogen

24
Q

What are tertiary halogenoalkanes?

A

0 hydrogens attached to the carbon with the halogen

25
Q

What are nucleophiles?

A

Electron pair donors

26
Q

What are some examples of nucleophiles?

A

Ammonia, cyanide and hydroxide ions

27
Q

What are the conditions for the nucleophilic substitution with hydroxide ions?

A

Dissolve halogenoalkane in ethanol and add aqueous solution of sodium hydroxide and reflux gently

28
Q

What are the conditions for the nucleophilic substitution with cyanide ions?

A

Dissolve halogenoalkanes in ethanol and add solution of potassium cyanide and reflux gently

29
Q

What are the conditions for the nucleophilic substitution with ammonia ions?

A

Dissolve halogenoalkanes in a small volume of ethanol and add concentrated solution of ammonia in excess and put it into a sealed container under pressure

30
Q

How does ammonia increase the yield of a primary amine?

A

Stops the halogenoalkane from reacting with the primary amine, so it reacts with the ammonia and forms more primary amines

31
Q

What is a primary amine?

A

Amine with the N having two hydrogens and one R group

32
Q

What is a secondary amine?

A

N atom has two R groups

33
Q

What is a tertiary amine?

A

N atom has three R groups

34
Q

What does a halogenoalkane form when it has undergone elimination?

A

Alkene, halide ion and water

35
Q

What are the conditions for a substitution reaction when OH- ions are present?

A

OH dissolved in water
Sodium hydroxide
Room temp
Primary halogenoalkanes

36
Q

What are the conditions for an elimination reaction when OH- ions are present?

A

Hydroxide dissolved in ethanol
Potassium hydroxide is used
Mixture heated strongly
Tertiary halogenoalkanes

37
Q

Name some of the uses of halogenoalkanes?

A

Herbicides, insecticides, anaesthetic and solvent

AS Chemistry (14 decks)

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