4.4 Alcohols

Question 1

What is the functional group alcohols ?

Answer 1

OH, known as the hydroxyl group, which is responsible for physical and chemical properties of the alcohol.

Question 2

Are alcohol molecules polar or non-polar ?

Answer 2

They are polar due to polar O-H bonds due to difference in electronegativity values. So London forces are weak but hydrogen bonds are strong.

Question 3

What are the physical properties of alcohols compared to their alkane counterparts ?

Answer 3

Alcohols are less volatile, have higher boiling points and greater solubility than alkane counterparts.

Question 4

What is the boiling point in alcohols ?

Answer 4

Hydrogen bonds hold alcohol molecules together, which must be broken for alcohol to turn into a gas, which requires more energy to break hydrogen bonds than energy to break London forces.

Question 5

Are alcohols soluble in water ?

Answer 5

Alcohols are soluble in water as hydrogen bonds can form between polar OH group in the alcohols and water molecules.

Question 6

Is solubility affected as chain length increases in alcohols ?

Answer 6

As chain length increases, influence of OH functional group becomes smaller, so solubility decreases.

Question 7

What is a primary alcohol ?

Answer 7

Alcohol with 0 or 1 alkyl group attached to the carbon atom with the OH bonded to it.

Question 8

What is a secondary alcohol ?

Answer 8

Alcohol with 2 alkyl groups attached to carbon atom with OH bonded to it.

Question 9

What is a tertiary alcohol ?

Answer 9

Alcohol with 3 alkyl groups attached to carbon atom with OH bonded to it.

Question 10

Is combustion of alcohols exothermic or endothermic ?

Answer 10

The reaction is exothermic, releasing a large quantity of energy in the form of heat, when producing CO2 and H2O. As the number of carbon atoms in alcohol chain increases, quantity of heat released per mole increases.

Question 11

What is the conditions for oxidation of alcohols ?

Answer 11

Alcohols can be oxidised by heating alcohol with potassium dichromate and dilute sulphuric acid.

Question 12

What is the colour change observed in oxidation of alcohols ?

Answer 12

Orange to green.

Question 13

What is the oxidising mixture represented as ?

Answer 13

[O] and multiple number of oxygens can be shown as 2[O].

Question 14

What do primary alcohols form in oxidation reaction ?

Answer 14

Forms and aldehyde and then a carboxylic acid, when it is oxidised further.

Question 15

What do secondary alcohols form in oxidation reaction ?

Answer 15

Forms a ketone.

Question 16

What do tertiary alcohols form in oxidation reaction ?

Answer 16

There is no reaction.

Question 17

How are aldehydes prepared ?

Answer 17

An aldehyde is distilled out of the mixture as it is formed as this prevents it oxidising further into a carboxylic acid.

Question 18

How are carboxylic acids prepared ?

Answer 18

When an alcohol is heated under strong reflux with excess potassium dichromate , all the alcohol is oxidised. Reflux ensures that all the aldehyde is formed when alcohol is first oxidised turns into carboxylic acid.

Question 19

What is the dehydration reaction of alcohols ?

Answer 19

Where a water molecule is removed from the alcohol. It is an example of an elimination reaction, where a smaller molecule is removed from a larger molecule, forming 2 products.

Question 20

What are the conditions for a dehydration reaction of alcohols ?

Answer 20

The alcohol is heated under reflux with an acid catalyst, such as concentrated sulphuric acid.

Question 21

What atoms are being removed from alcohol in dehydration reaction ?

Answer 21

The OH functional group and a hydrogen atom adjacent to the OH function group, but that is not attached to the same carbon atom.

Question 22

What is the substitution reaction of alcohols ?

Answer 22

Alcohols react with hydrogen halides to form haloalkanes. The hydrogen halide in formed first, and then reacts with the alcohol.

Question 23

What are the conditions for a substitution reaction of alcohols ?

Answer 23

The alcohol is heated under reflux with dilute sulphuric acid and a sodium halide to form a hydrogen halide. Then the hydrogen halide reacts with the alcohol.