14.1(4.2.1) - Alcohols

Question 1

Functional group of alcohols

Answer 1

-OH

Question 2

What is the functional group called and what does it effect?

Answer 2

Known as hydroxyl group

Responsible for both the physical and chemical properties of the alcohols

Question 3

Suffix for alcohols

Answer 3

-ol added to some name of longest carbon carbon chain

Question 4

Physical properties of alcohols

Answer 4

Have a polar O-H bond because of difference in electronegativity of oxygen and hydrogen atoms
Alcohol molecules are therefor polar
Intermolecular forces will be very weak London Forces
Also much stronger hydrogen bonds between polar O-H groups

Question 5

Boiling point and volatility of alcohols

Answer 5

In liquid state, intermolecular hydrogen bonds hold alcohol molecules together.
These bonds must be broken in order to change liquid alcohol into a gas.
This requires more energy
So alcohols have a lower volatility(evaporate less easily)

Question 6

BP and volatility of alcohols compared to alkanes

Answer 6

Alcohols require more energy to break strong hydrogen bonds
More energy than overcoming weaker London forces in alkanes
Therefore alkanes have a higher volatility than alcohols with same no. of carbon atoms

Question 7

Solubility of alcohols in water

Answer 7

Alcohols are polar molecules so can form bonds with water molecules by hydrogen bonding
Hydrogen bond forms from polar -OH group of alcohol and water molecules

Question 8

Solubility of alkanes in water

Answer 8

Alkanes are non-polar molecules

So cannot from hydrogen bonds with water

Question 9

Solubility of alcohols with increasing chain length

Answer 9

As alcohols hydrocarbon chains become larger
Influence of the -OH group becomes relatively smaller
Solubility decreases as hydrocarbon chains increase

Question 10

Three classifications for alcohols

Answer 10

Primary
Secondary
Tertiary

Question 11

How to classify primary alcohols

Answer 11

When the -OH group is attached to a carbon attached to one other carbon
E.g. methanol

Question 12

Classifying secondary alcohols

Answer 12

When the alkyl(-OH) group is attached to a carbon attached to two other carbons
E.g. propan-2-ol

Question 13

Classifying tertiary alcohols

Answer 13

When the -OH group is attached to a carbon atom which is a attached to three other carbon atoms
E.g. 2-methylpropan-2-ol

Question 14

Combustion of alcohols

Answer 14

Alcohols burn completely in a plentiful supply of oxygen to produce:
Carbon dioxide
Water
Reaction is exothermic - releases lots of energy in form of heat
As chain length of alcohol increases, so does amount of energy released

Question 15

Oxidising agent for oxidation of alcohols

Answer 15

Acidified Potassium dichromate,

K2Cr2O7.H2SO4

Question 16

What is an oxidising agent?

Answer 16

A substance that tends to bring about oxidation by being reduced and gaining electrons

Question 17

Different forms alcohols go to when oxidised

Answer 17

Alcohol - e.g. butan-1-ol
Aldehyde - butanal
Carboxylic acid - butanoic acid

Question 18

Prep of aldehydes from alcohols

Answer 18

Gentle heating of primary alcohols with acidified potassium dichromate
Aldehyde is distilled out of reaction mixture as it forms to ensure no further reactions occur with oxidising agent
Dichromate ions change colour from orange to green

Question 19

Preparation of carboxylic acids

Answer 19

Heating primary alcohol strongly under reflux, with excess of acidified potassium dichromate
Use of excess ensures all alcohol is oxidised
Heating under reflux ensures any aldehyde formed in reaction also undergoes oxidation to carboxylic acid

Question 20

What signifies oxidation in an equation?

Answer 20

When an arrow product arrow has ‘[O]’ on it

Question 21

Conditions for different oxidations of alcohols

Answer 21

When preparing aldehyde use distillation to remove the aldehyde from reaction mixture
When preparing carboxylic acid, heat alcohol under reflux

Question 22

Products from oxidation of secondary alcohols

Answer 22

Secondary alcohols are oxidised to ketones

Question 23

Oxidising secondary alcohols process

Answer 23

To ensure reaction goes to completion, secondary alcohol is heated under reflux with oxidising mixture
Dichromate ions change colour from orange to green

Question 24

Example of formation of ketone from secondary alcohol

Answer 24

Propan-2-ol + [O] —> propanone

Question 25

Oxidation of tertiary alcohols

Answer 25

They do not undergo oxidation reactions.

The acidified dichromate remains orange when added to a tertiary alcohol