Unit 3 - Alcohols & Carboxylic Acids

Question 1

Structure of Alcohols

Answer 1

The functional group in an alcohol is the hydroxyl group (-OH). The general formula for the alcohol homologous series is CnH2n+1OH

In straight chain alcohols with more than 3 carbon atoms, the position of the hydroxyl group is indicated in the named.

In branched chain alcohols, the main chain is the longest chain which includes the hydroxyl group

Question 2

Types of Alcohol: Primary

Answer 2

In a primary alcohol, no more than one carbon atom is joined directly to the carbon bonded to the hydroxyl group.

Question 3

Types of Alcohol: Secondary

Answer 3

In a secondary alcohol, there are two carbon atoms attached to the carbon bonded to the hydroxyl group.

Question 4

Types of Alcohols: Tertiary

Answer 4

In a tertiary alcohol, there are three carbon atoms attached to the carbon bonded to the hydroxyl group.

Question 5

Physical Properties of Alcohols: Boiling Point

Answer 5

All alcohols have similar chemical properties. As the size of the molecule increases, the boiling points increase.

The boiling point of an alcohol is relatively high compared to the corresponding alkane. This i because hydroxyl groups make alcohols polar and this gives rise to hydrogen bonding between alcohol molecules.

Question 6

Physical Properties of Alcohols: Solubility

Answer 6

Smaller alcohols are soluble in water because the hydroxyl group can form hydrogen bonds with water. Larger alcohols are insoluble due to the influence of the non-polar hydrocarbon chain.

Question 7

Diols and Triols

Answer 7

Some alcohols contain more than one hydroxyl group in the molecule e.g. antifreeze contains ethan-1,2-diol (ethylene glycol), fats and oils can be hydrolysed to produce propane-1,2,3-triol (glycerol)

Question 8

Alcohols, Boiling Points and Hydrogen Bonding

Answer 8

Alcohols with a greater number of hydroxyl groups have even higher boiling points. The large increase in the boiling point of alcohols as the number of hydroxyl groups increases is caused by a greater degree of hydrogen bonding.

The greater degree of hydrogen bonding also accounts for the increase in viscosity as the number of hydroxyl groups increases.

Question 9

Structure of Carboxylic Acids

Answer 9

The functional group in a carboxylic acid is the carboxyl group (-COOH)

In branched chain carboxylic acids, the main chain is the longest chain which includes the carboxyl group.