4.4 - Alcohols

Question 1

What is the functional group of an alcohol

Answer 1

-OH

Question 2

What is the general formula of an alcohol

Answer 2

CnH2n+1OH

Question 3

why are there hydrogen bonds in alcohols

Answer 3

Due to the O-H bond which is very electronegative

Question 4

What is the trend in alcohols with MP and BP and why

Answer 4

the longer the chain the higher the BP as there are more induced dipole-dipole forces this means that more energy is required to overcome the bonds.

Question 5

What is the solubility in alcohols

Answer 5

Small alcohols are soluble in water
however long length chains are not soluble in water

Question 6

are alcohols more or less volatile then their alkane counterpart

Answer 6

less

Question 7

What is a primary alcohol

Answer 7

The -OH group is attached to a carbon that is attached to one alkyl group and 2 hydrogen atoms (methanol is an exception but still primary)

Question 8

what is a secondary alcohol

Answer 8

The -OH group is attached to a carbon that is attached to 2 alkyl groups and 1 hydrogen atom

Question 9

what is a tertiary alcohol

Answer 9

○ The -OH group is attached to a carbon that is attached to 3 alkyl groups and no hydrogen atoms

Question 10

What is the word equation for combustion of alcohols

Answer 10

Alcohol + Oxygen -> CO2 + water

Question 11

Which alcohols can be Oxidised

Answer 11

Primary and Secondary

Question 12

What is the usual oxidising agent

Answer 12

a solution of potassium dichromate[K2Cr2O7] acidified with dilute sulfuric acid[H2SO4]

Question 13

What colour change do you see when an alcohol is oxidised

Answer 13

orange to green

Question 14

What can primary alcohols form when oxidised

Answer 14

Aldehydes or carboxylic acids

Question 15

What can secondary alcohols form when oxidised

Answer 15

Ketones

Question 16

How do you prepare an aldehyde from an alcohol

Answer 16

Gently heat a primary alcohol with the [O]
To ensure an aldehyde is formed it is distilled out of the reaction mixture as it is formed to prevent further reaction
The [O] changes colour from orange to green

Question 17

How do you prepare a carboxylic acid from an alcohol

Answer 17

Heat a primary acid strongly under reflux with an excess of acidified potassium dichromate a carboxylic acid is formed.
Excess [O] ensures all of the alcohol is oxidised
The reflux ensures any aldehyde formed initially in the reaction also undergoes oxidation

Question 18

How do you prepare a ketone from a secondary alcohol

Answer 18

Heat with [O]
To ensure reaction goes to completion the secondary alcohol is heated under reflux
Orange to green colour change

Question 19

what happens when you try to oxidise tertiary alcohols

Answer 19

Do not undergo oxidation
[O] stays orange

Question 20

What is the elimination reaction of alcohols known as

Answer 20

Dehydration of alcohols

Question 21

What molecule is removed in the dehydration of alcohol

Answer 21

H2O

Question 22

What catalyst is used in the dehydration of alcohols

Answer 22

Concentrated sulfuric acid or phosphoric acid

Question 23

What is the word equation for the dehydration of alcohols

Answer 23

Alcohol + acid catalyst -> alkene + water

Question 24

in the substitution reaction of alcohols what molecule is substituted

Answer 24

The -OH group is replaced by a Halogen

Question 25

What is the word equation + conditions for the reaction of alcohols to form haloalkanes

Answer 25

Alcohol + hydrogen halide -> Haloalkane + water
alcohol is heated under reflux with sulfuric acid and a sodium halide the hydrogen halide is formed in place here
eg. NaBr + H2SO4 -> NaHSO4 + HBr
the hydrogen halide formed here reacts with the alcohol to form a haloalkane