A solution of gaseous methylamine, CH3NH2, turns red litmus blue. Write the equation and explain this observation.
Doesn't the -NH2 act like a proton donor?
To understand why a solution of gaseous methylamine (CH3NH2) turns red litmus blue, we need to consider the properties of methylamine and litmus.
First, let's write the equation for the reaction that takes place:
CH3NH2 + H2O → CH3NH3+ + OH-
In this reaction, the methylamine (CH3NH2) reacts with water (H2O) to form a positively charged methylammonium ion (CH3NH3+) and a hydroxide ion (OH-).
Now, let's understand the observation. Litmus is a natural dye that is extracted from lichens. It exists in two forms: red litmus and blue litmus. Red litmus is red in an acidic solution and remains red in a neutral or basic solution. However, when it is exposed to an alkaline (basic) solution, it turns blue.
Methylamine is a weak base. When it dissolves in water, it acts as a base by accepting a proton (H+) from water. This forms the methylammonium ion (CH3NH3+), which is capable of alkaline behavior. The hydroxide ion (OH-) produced in the reaction also contributes to the basic nature of the solution.
When a red litmus paper is dipped into the solution of gaseous methylamine, the litmus paper comes into contact with the basic solution. As a result, the red litmus paper changes its color from red to blue. This color change indicates that the solution is alkaline.
In summary, the solution of gaseous methylamine turns red litmus blue because methylamine is a weak base, and its reaction with water produces hydroxide ions, making the solution alkaline or basic in nature.