Question

[(a)] What happens when propanoic acid is warmed with methanol in the presence of a few drops of sulphuric acid? Write an equation of the reaction involved.
$(b)$ What changes will you observe if you test soap solution with a litmus paper (red and blue)? Give reason for your observation.
$(c)$ What is meant by denatured alcohol? What is the need to denature alcohol?

Answer 1

For the question use the molecular formula of propanoic acid which is $C{H_3}C{H_2}COOH$. This concept along with the basis of carbon that only four outermost valence electrons are present in carbon and this need to be satisfied for every carbon atom will help in getting the right structural formula.

Complete answer:
$(a)$ When propanoic acid is warmed with methanol in the presence of a few drops of concentrated sulphuric acid in it, esterification takes place and an ester named methyl propanoate is formed along with water. The chemical equation for the above reaction is:
${C_2}{H_5}COOH + C{H_3}OH \to {C_2}{H_5}COOC{H_3} + {H_2}O$
$(b)$ Soap is the salt of a strong base (sodium hydroxide) and a weak acid (carboxylic acid). Hence, its solution with water is also basic in nature. Therefore, it will turn red litmus paper to blue and there will be no change observed in blue litmus paper as the soap solution is basic.
$(c)$ Denatured alcohol is ethyl alcohol which has been made unfit for drinking purposes by adding small amounts of poisonous substances like methanol, pyridine, copper sulphate etc. this is done to prevent the misuse of industrial alcohol for drinking purposes or black marketing (as it is supplied duty-free for industrial purposes).

Note:
As normal alcohol and denatured alcohol both are transparent, denatured alcohol is mostly colored to identify it distinctively. Consumption of denatured alcohol can be lethal, it can cause severe damage and possibly death.