Question

What would you observe when :

(a) blue litmus is introduced into a solution of hydrogen chloride gas,

(b) red litmus paper is introduced into a solution of ammonia in water,

(c) red litmus paper is introduced in caustic soda solution?

Answer 1

(a) $HCl$ is acidic in nature. So, when the Hydrogen chloride solution is introduced to a blue litmus. Then, blue litmus will turn into red showing the acidic nature of the Hydrogen chloride gas.
Note: When dry gas is brought near the dry blue litmus no effect will be observed. For the effects to be observed, either the gas should be in the forms of a solution or the litmus will be moist.

(b) When $N{H}_3$ reacts with water, $N{H}_{4}OH$(ammonium hydroxide) is formed which is a base and it contains $N{H}^{4+}$ ion and $O{H}^{-}$ ion. Since basic ion is present, hence it changes the red litmus paper blue.

(c)Turn red litmus paper blue