Halogenoalkanes (MDY)

Question 1

Are haloalkanes saturated or unsaturated?

Answer 1

Saturated

Question 2

General formula of haloalkanes

Answer 2

CnH2n+1X

Question 3

Are haloalkanes polar?

Answer 3

Yes

Question 4

Which bond in a haloalkane is polar and why?

Answer 4

C - X bond because X is more electronegative than C and attracts electrons towards it more strongly.

Question 5

Why aren’t haloalkanes water soluble?

Answer 5

C - X bond is not polar enough to disrupt the IMFs in water

Question 6

What type of reactions do haloalkanes undergo?

Answer 6

Nucleophilic sub and elimination

Question 7

Why does chloromethane have a higher melting point than methane?

Answer 7

It has a higher molecular mass so it has more electrons and it’s VdW forces are stronger and harder to break

Question 8

What is a primary haloalkane?

Answer 8

One where X is bonded to a carbon that is bonded to one other alkyl group

Question 9

What is a secondary haloalkane?

Answer 9

One where X is bonded to a carbon that is bonded to 2 other alkyl groups

Question 10

What is a tertiary haloalkane?

Answer 10

One where X is bonded to a carbon that is bonded to 3 other alkyl groups

Question 11

What is a nucleophile?

Answer 11

An electron rich species that can donate a pair of electrons

Question 12

What is a nucleophilic substitution reaction?

Answer 12

One where a halogen is substituted for a nucleophile

Question 13

Describe what happens during a general nucleophilic substitution reaction.

Answer 13

Lone pair on the nucleophile is attracted to the delta positive charge on the carbon. C - X bond breaks heterolytically, forming a halide ion

Question 14

Conditions for nucleophilic substitution with OH-

Answer 14

Warm aqueous NaOH. Dissolve reaction mixture in ethanol to make haloalkane miscible

Question 15

Products of nucleophilic sub with OH-

Answer 15

Alcohol, NaX and halide

Question 16

Conditions for nucleophilic substitution with CN-

Answer 16

Warm, ethanolic KCN

Question 17

Products of nucleophilic sub with CN-

Answer 17

Nitrile, KX and halide

Question 18

Conditions for nucleophilic substitution with NH3-

Answer 18

Excess, concentrated ethanolic ammonia at high pressure in a sealed container

Question 19

Products of nucleophilic sub with NH3-

Answer 19

Primary amines, ammonium ion and hydrogen halide

Question 20

Conditions for elimination:

Answer 20

Warm ethanolic concentrated NaOH/KOH

Question 21

What happens during an elimination reaction?

Answer 21

OH- are attracted to the C next to the C-X bond
C - H breaks to form C=C
CX breaks by heterolytically

Question 22

Products of elimination

Answer 22

Alkene, water and NaX or KX

Question 23

What determines the ease of substitution of a haloalkane and how?

Answer 23

C - X Bond enthalpy, lower bond enthalpy means weaker bond, more reactive haloalkane and easier substitution

Question 24

Which has a higher bond enthalpy and why, C - F or C - Br?

Answer 24

C - F because F is more electronegative than Br so the dipole is stronger and harder to break

Question 25

Reaction between haloalkanes and aqueous AgNO3

Answer 25

Haloalkane + Water + AgNO3 --> Alcohol + H+ + X-

Question 26

What colour is silver chloride?

Answer 26

White

Question 27

What colour is silver bromide?

Answer 27

Cream

Question 28

What colour is silver iodide?

Answer 28

Pale Yellow

Question 29

Steps to testing for haloalkanes:

Answer 29

1. Reflux wit NaOH to release X- ions 2. Add any excess nitric acid to neutralise excess OH- 3. Add AgNO3 which will identify the halogen by the colour of the precipitate 4. Follow up test using dilute and concentrated NH3

Question 30

Why do you need to neutralise any excess OH-

Answer 30

OH- will react with Ag+ to create brown silver hydroxide which will interfere with the test

Question 31

Why can't you use HCl or Sulphuric acid to neutralise excess OH-

Answer 31

They will create white precipitates and interfere with the test

Question 32

Dilute and concentrated NH3 test:

Answer 32

AgCl will dissolve in both AgBr will dissolve in concentrated only AgI won't dissolve