Alcohols (F6examonly)

Question 1

Why do alcohols have high melting points and low volatility compared to alkanes?

Answer 1

• there is hydrogen bonding between the OH groups of alcohol molecules
• there are london forces between alkane molecules
• hydrogen bonding is stronger than london forces
• this means that alcohols require more energy to overcome these london forces
• and so have a higher melting point and lower volatility

Question 2

What is volatility?

Answer 2

how readily a substance vaporises (turns form a liquid into a gas)

Question 3

Why are alcohols soluble in water? Describe the trend of solubility:

Answer 3

• alcohol molecules can form hydrogen bonds with water molecules due to their OH group
• however the alkyl part of an alcohol cannot form hydrogen bonds
• therefore solubility decreases as the carbon chain gets longer

Question 4

What are primary, secondary, and tertiary alcohols?

Answer 4

• primary: the OH group is bonded to a carbon that is only bonded to one other carbon
• secondary: the OH group is bonded to a carbon that is bonded to two other carbons
• tertiary: the OH group is bonded to a carbon that is bonded to three other carbons

Question 5

Describe the combustion of alcohols:

Answer 5

• alcohols react with O2 to produce CO2 and H2O
• alcohols burn more cleanly than alkanes of similar lengths
• this is because they already contain an oxygen in the OH group, so require less oxygen from the air