Question

You are provided with two reagent bottles marked A and B. One of which contains NH4OH solution and the other contains NaOH solution. How will you identify them by a chemical test?

Answer 1

Reagent bottles A and B can identified by using calcium salts such as Ca(NO3)2.

On adding NaOH to Ca (NO3)2, Ca (OH) 2 is precipitated as white precipitate which is sparingly soluble in excess of NaOH.

Ca(NO3)2 + 2NaOH⟶ Ca(OH)2 + 2NaNO3

Whereas, on addition of NH4OH to calcium salts, no precipitation of Ca(OH)2 occurs even with addition of excess of NH4OH because the concentration of OH-ions from the ionization of NH4OH is so low that it cannot precipitate the hydroxide of calcium.

So the reagent bottle which gives white precipitate is NaOH and the other is NH4OH.