JAMB Chemistry 1980 Question 38

Question 38

Alkanals and Alkanones

A mixture of ethanol, sodium dichromate, and water is allowed to drop gradually into a boiling solution containing one part concentrated H₂SO₄ and three parts water, and the liberated gas is collected by cooling it with ice water to give a liquid. This liquid is

A.ethanoic acid
B.acetaldehyde
C.ethyl acetate
D.methanol
E.ethylene

Show the answer and explanation

Answer: B (acetaldehyde)

Explanation

Acidified dichromate oxidises ethanol first to ethanal (acetaldehyde), which boils at about 21°C. In the boiling mixture it escapes as a vapour before it can be oxidised further, and it condenses to a liquid in ice water.