Question

A solution of methylamine
A. Turn blue litmus red
B. Turn red litmus blue
C. Does not affect red or blue litmus
D. Bleaches litmus

Answer 1

Hint: Litmus paper tests are made to find the acidic and basic nature of compounds or solution. There are two litmus papers, red and blue. Acidic solutions affect only blue litmus paper (turn red) whereas basic solutions affect red litmus paper (turn blue).

Complete Step by Step Solution:
Methyl amine is the derivative of ammonia i.e. after replacing any one of hydrogen from ammonia (NH₃) by any alkyl group (say methyl), the derivative of ammonia, methyl amine (CH₃NH₂).

Ammonium is a Lewis base because of presence of lone pair on nitrogen thus its derivative, methyl amine also has tendency to give its lone pair of electrons to any electron deficient species or can say methyl is Lewis base.

As per hint, base always affects red litmus paper by changing colour to blue. And it does not turn blue litmus red which is for acid solution. For bleaches litmus, solution of methyl amine will not show any effect as effective beaches is itself an acidic solution (chlorine + water).
Thus, the correct answer is B, turn red litmus blue because of the basic nature of the solution of methylamine.

Note: Any substance is said to be base when it has tendency to give electrons as per Lewis base. While bases are also those substances which can easily release OH^- in aqueous solution or can accept H⁺ from acid. Thus, methyl amine with its lone pair of electrons acts as Lewis acid.