Question

The salt solution that does not react with ammonium hydroxide is:
A. Calcium nitrate
B. Zinc nitrate
C. Lead nitrate
D. Copper nitrate

Answer 1

Hint: Think about the nature of ammonium hydroxide and what will happen if it reacts with a salt in an aqueous medium and what kind of precipitate would be formed.

Complete answer:
Ammonium hydroxide can be formed by adding ammonia to water. It is a weak base with the chemical formula of $N{{H}_{4}}OH$. Let us see what happens when it is added to each of the salts given.
A. Calcium nitrate
When ammonium hydroxide is added to calcium nitrate, no reaction or formation of precipitate is seen. An excess of ammonium hydroxide also does not show any results.
Since, ammonium hydroxide is a weak acid, it is very difficult for the $O{{H}^{-}}$ions to displace the $N{{O}_{3}}^{2-}$ ions in calcium nitrate.
B. Zinc nitrate
When ammonium hydroxide is added to zinc nitrate, a white, gelatinous precipitate is formed. This precipitate dissolves in excess of ammonium hydroxide. The reaction is as follows:
\[Zn{{(N{{O}_{3}})}_{2}}+2N{{H}_{4}}OH\to Zn{{(OH)}_{2}}+2N{{H}_{4}}N{{O}_{3}}\]
C. Lead nitrate
When ammonium hydroxide is added to lead nitrate, a chalky white precipitate is obtained. The precipitate does not dissolve in excess of ammonium hydroxide. The reaction is as follows:
\[Pb{{(N{{O}_{3}})}_{2}}+2N{{H}_{4}}OH\to Pb{{(OH)}_{2}}+2N{{H}_{4}}N{{O}_{3}}\]
D. Copper nitrate
When ammonium hydroxide is added to copper nitrate, a pale blue precipitate is obtained. The addition of excess ammonium hydroxide will give a dark, inky blue solution. The reaction is as follows:
\[Cu{{(N{{O}_{3}})}_{2}}+2N{{H}_{4}}OH\to Cu{{(OH)}_{2}}+2N{{H}_{4}}N{{O}_{3}}\]

Hence, we can see that the correct answer is ‘A. Calcium nitrate’

Note: Please remember that although ammonium hydroxide does not react with calcium nitrate, it does react with magnesium nitrate. There is no rule according to which ammonium hydroxide reacts with alkali metals and alkaline earth metals.