Alcohols

Question 1

In a preparation of propanal, propan-1-ol is added dropwise to the oxidising agent and the aldehyde is separated from the reaction mixture by distillation.
Explain, with reference to intermolecular forces, why distillation allows propanal to be
separated from the other organic compounds in this reaction mixture.

Answer 1

• Aldehyde/propanal has dipole-dipole forces (between molecules)
• Alcohol/propan-1-ol AND Carboxylic acid/ propanoic acid have
• hydrogen bonding (between molecules).
• The forces between the molecules in aldehyde are weaker (than M3 those in alcohol and acid so it will evaporate first.)

Question 2

Give two ways of maximising the yield of propanal obtained by distillation of the
reaction mixture

Answer 2

Keep the temperature of the reaction mixture below the boiling point of propan-1-ol/below 97 °C
Cool the distillate / collecting vessel

Question 3

Describe how you would carry out a simple test-tube reaction to confirm that the sample of propanal obtained by distillation does not contain any propanoic acid.

Answer 3

• Add named carbonate/hydrogencarbonate OR magnesium to a sample of the distillate.
• Effervescence/fizz/bubbles would confirm presence of acid or

Question 4

Suggest how the anti-bumping granules prevent bumping during reflux.

Answer 4

prevents larger bubbles forming

Question 5

Suggest why an electric heater is used rather than a Bunsen burner in this hydrolysis

Answer 5

many organic compounds are flammable (specify)

Question 6

State why reflux is used in this hydrolysis

Answer 6

does not allow reactant vapour to escape