Question

(a) What is a homologous series of compounds? List any two characteristics of a homologous series.
(b) (i) What would be observed on adding a 5% alkaline potassium permanganate solution drop by drop to some warm ethanol in a test tube?
(ii) Write the name of the compound formed during the chemical reaction.
(c) How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis of a chemical property?

Answer 1

(a) A homologous series is a series of organic compounds, which differ by a same repeating unit and have similar chemical properties due to the presence of the same functional group.

Characteristics of homologous series:
(i) Two consecutive members of a homologous series differ by a (-CH₂) unit and a mass of 14 amu.
(ii) Homologs of a series have similar chemical properties.

(b) (i) When 5% alkaline potassium permanganate is added to warm ethanol, ethanol gets oxidize to form ethanoic acid.

${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{\mathrm{alk}.{\mathrm{KMnO}}_4}{\to }{\mathrm{CH}}_3\mathrm{COOH}$

(ii) The compound formed during the reaction is ethanoic acid.

(c) Carboxylic acids react with sodium bicarbonate to produce brisk effervescence due to the release of carbon dioxide gas, whereas alcohols do not react with sodium bicarbonate.