Action of Ammonium Hydroxide on Metallic Salt Solutions: Elements in chemical compounds are identified by certain analyses. In chemistry, two types of analysis are there: Quantitative Analysis and Qualitative Analysis. Quantitative analysis is done for determining the composition, whereas Qualitative analysis is done to identify the unknown substance present in the mixture. Such analysis is performed by carrying out chemical tests using certain reagents, and one of the essential laboratory reagents are “alkalis”. Apart from chemical tests, physical tests include identifying an unknown substance based on specific physical properties like colour, solubility, or texture.

Ammonium hydroxide is a base, and when this base is added to the metallic salt solution, metal hydroxide gets precipitated out. The colour, as well as the solubility of the precipitate when an excess of ammonium hydroxide is added, gives an obvious idea about the identification of the metal ion present in that metallic salt solution. In this article, we will try to go through the different chemical reactions involved when ammonium hydroxide reacts with metallic salt solutions.

What is Ammonium Hydroxide?

Ammonium hydroxide is also known as an aqueous solution of ammonia, \({\text{N}}{{\text{H}}_3}\) or a solution of ammonia in the water. It is denoted by the symbols \({\text{N}}{{\text{H}}_3}\,\left( {{\text{aq}}} \right)\) or chemical formula \({\text{N}}{{\text{H}}_4}{\text{OH}}\). As the name ‘ammonium hydroxide’ suggests, it is an alkali having composition \(\left[ {{\text{NH}}_4^ + } \right]\,\left[ {{\text{O}}{{\text{H}}^ – }} \right]\).

In the aqueous solution, a minute fraction of the water is deprotonated by Ammonia to give ammonium and hydroxide ions as given in the equilibrium equation below:

\({\text{N}}{{\text{H}}_3}{\mkern 1mu} + {\mkern 1mu} {{\text{H}}_2}{\text{O}} \rightleftharpoons {\mkern 1mu} {\text{NH}}_4^ + {\mkern 1mu} + {\mkern 1mu} {\text{O}}{{\text{H}}^ – }\)

Difference Between Sodium Hydroxide and Ammonium Hydroxide

Some of the basic differences between Sodium hydroxide and Ammonium hydroxide are as follows:

1. Both Sodium hydroxide \(\left( {{\text{NaOH}}} \right)\) and Ammonium hydroxide \(\left( {{\text{N}}{{\text{H}}_4}{\text{OH}}} \right)\) are alkalis but Sodium hydroxide is a strong base while Ammonium hydroxide is a weak base.
2. Ammonium hydroxide exists in liquid state while sodium hydroxide exists in solid-state at room temperature.
3. Ammonium ions react with sodium hydroxide because ammonium hydroxide is a weaker base than sodium hydroxide. The ammonium hydroxide formed in this reaction is further decomposed to evolve ammonia gas. For example, Ammonium chloride can react with sodium hydroxide to form ammonia gas \(\left( {{\text{N}}{{\text{H}}_3}} \right)\), water, and sodium chloride \(\left( {{\text{NaCl}}} \right)\).
4. A very easily detectable feature of these two alkalis is that ammonium hydroxide has a fishy, pungent odour while sodium hydroxide has no smell at all, i.e., it is odourless.

Examples of the Action of Ammonium Hydroxide on Metallic Salt Solutions

Generally, the reaction of Ammonium hydroxide solution with metallic salt solution results in metal hydroxide as a precipitate along with the salt solution. The general chemical equation of this chemical reaction is represented as:

\({\text{Metallic}}\,{\text{Salt}}\, + \,{\text{Ammonium}}\,{\text{Hydroxide}}\, \to\,{\text{Metal hydroxide}}\)
\({\text{ + Salt formed in the solution}}\)

1. Reaction of Calcium ion with Ammonium Hydroxide
   Calcium ions  \({\text{C}}{{\text{a}}^{2 + }}\) does not react with ammonium hydroxide as ammonium hydroxide is a weak base, thus on ionization it forms low concentration of \({\text{O}}{{\text{H}}^ – }\) ions. As the concentration of \({\text{O}}{{\text{H}}^ – }\) ions are quite low as a result of the ionisation of \({\text{N}}{{\text{H}}_4}{\text{OH}}\), it cannot react with calcium salt to form the precipitate of calcium hydroxide.
   
   \({\text{C}}{{\text{a}}^{2 + }}\, + \,{\text{N}}{{\text{H}}_4}{\text{OH}}\, \to \,{\text{No Reaction}}\)
   
   
2. Reaction of Ferrous Sulphate with Ammonium Hydroxide
   Ferrous Sulphate is a metallic salt solution of Iron that is pale-green in colour and that reacts with ammonium hydroxide when it is introduced in drop-wise manner to the solution of ferrous sulphate and form a green precipitate of ferrous hydroxide along with ammonium sulphate, which is colourless. On adding excess of ammonium hydroxide to this precipitate, ferrous hydroxide is insoluble. The chemical reaction carried out in this process is denoted by the following chemical equation:
   
   \({\text{FeS}}{{\text{O}}_4}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}}\, \to \,{\text{Fe}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + \,{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\)
   
   
3. Reaction of Ferric salt or Ferric Chloride with Ammonium Hydroxide
   When ammonium hydroxide solution is added drop-wise to the solution of ferric chloride, it undergoes chemical reaction with ammonium hydroxide to form a reddish-brown precipitate of ferric hydroxide along with ammonium chloride, which is colourless. When an excess amount of ammonium hydroxide is introduced into this precipitate, ferrous hydroxide is not soluble at all. The chemical reaction that is involved in this process is denoted by the following chemical equation:
   
   \({\text{FeC}}{{\text{l}}_3}\, + \,3{\text{N}}{{\text{H}}_4}{\text{OH}} \to \,{\text{Fe}}{\left( {{\text{OH}}} \right)_3} \downarrow \,3{\text{N}}{{\text{H}}_4}{\text{Cl}}\)
   
   \({\text{F}}{{\text{e}}_2}{\left( {{\text{S}}{{\text{O}}_4}} \right)_3}\, + \,6{\text{N}}{{\text{H}}_4}{\text{OH}}\, \to \,{\text{2Fe}}{\left( {{\text{OH}}} \right)_3} \downarrow \, + 3{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\)
   
   
4. Reaction of Copper Sulphate with Ammonium Hydroxide
   When ammonium hydroxide solution is added dropwise to the solution of copper sulphate, it reacts with ammonium hydroxide to form a pale-blue precipitate of copper hydroxide along with ammonium sulphate. The chemical reaction which is involved in this process is denoted by the following chemical equation:
   
   \({\text{CuS}}{{\text{O}}_4}\, + 2{\text{N}}{{\text{H}}_4}{\text{OH}} \to \,{\text{Cu}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + {\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\)
   
   On adding excess of ammonium hydroxide, copper hydroxide gets dissolved and form a deep blue coloured solution as shown below:
   
   \({\text{Cu}}{\left( {{\text{OH}}} \right)_{2\,}} + \,{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}} \to {\left[ {{\text{Cu}}\left( {{\text{N}}{{\text{H}}_3}} \right)} \right]_4}{\text{S}}{{\text{O}}_4}\, + \,4{{\text{H}}_2}{\text{O}}\)
   
   
5. Reaction of Zinc Sulphate with Ammonium Hydroxide
   When ammonium hydroxide solution is added dropwise to the solution of zinc sulphate, it reacts with ammonium hydroxide to form a white-gelatinous precipitate of zinc hydroxide along with ammonium sulphate. When an excess of ammonium hydroxide is added to this precipitate, zinc hydroxide gets solubilized. The chemical reaction involved in this process is denoted by the following chemical equation:
   
   \({\text{ZnS}}{{\text{O}}_4}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}} \to \,{\text{Zn}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + \,{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\)
   
   The same type of reaction occurs when zinc chloride reacts with ammonium hydroxide:
   
   \({\text{ZnC}}{{\text{l}}_2}\, + 2{\text{N}}{{\text{H}}_4}{\text{OH}} \to \,{\text{Zn}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + \,2{\text{N}}{{\text{H}}_4}{\text{Cl}}\)
   
   
6. Reaction of Lead Nitrate with ammonium hydroxide
   When ammonium hydroxide solution is added dropwise to the solution of lead nitrate, it reacts with ammonium hydroxide to form a chalky white precipitate of lead hydroxide along with ammonium nitrate. When an excess of ammonium hydroxide is added to this precipitate, lead hydroxide is insoluble. The chemical reaction involved in this process is denoted by the following chemical equation:
   
   \({\text{Pb}}{\left( {{\text{N}}{{\text{O}}_3}} \right)_2}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}} \to \,{\text{Pb}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + \,2{\text{N}}{{\text{H}}_4}{\text{N}}{{\text{O}}_3}\)
   
   
7. Reaction of Barium Chloride with Ammonium Hydroxide
   When ammonium hydroxide solution is added dropwise to the solution of barium chloride, it reacts with ammonium hydroxide to form a white precipitate of barium hydroxide along with ammonium chloride. The chemical reaction involved in this process is denoted by the following chemical equation:
   
   \({\text{BaC}}{{\text{l}}_2} + 2{\text{N}}{{\text{H}}_4}{\text{OH}} \to {\text{Ba}}{\left( {{\text{OH}}} \right)_2} \downarrow + 2{\text{N}}{{\text{H}}_4}{\text{Cl}}\)
   
   
8. Reaction of Magnesium Chloride with Ammonium Hydroxide
   When ammonium hydroxide solution is added dropwise to the aqueous solution of magnesium chloride, it reacts with ammonium hydroxide to form a solid, insoluble white precipitate of magnesium hydroxide along with ammonium chloride. The chemical reaction involved in this process is denoted by the following chemical equation:
   
   \({\text{MgC}}{{\text{l}}_2}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}}\, \to \,{\text{Mg}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + \,2{\text{N}}{{\text{H}}_4}{\text{Cl}}\)
   

All these chemical reactions are examples of double displacement reactions as two reactants exchange their ions to form entirely new compounds.

Summary

Thus, we have learnt that to identify unknown salts in the chemical laboratories; qualitative analysis is done. To identify metal ions, present in salt, metallic salts are reacted with ammonium hydroxide, and based on the colour and solubility of the precipitate in the presence of an excess of ammonium hydroxide gives us a clear identification of the metal ion present in that metallic salt solution. These reactions are mostly double displacement reactions, as both the ions exchange their positions. Such chemical reactions may also be called precipitation reactions as a precipitate of different colours, and textures are formed.

Some examples of the reaction of metallic salts with ammonium hydroxide are the reaction of ferrous sulphate with ammonium hydroxide to form ferrous hydroxide and ammonium sulphate, ferric chloride with ammonium hydroxide to form ferric hydroxide and ammonium chloride, lead nitrate with ammonium hydroxide to form lead hydroxide and ammonium nitrate, zinc chloride with ammonium hydroxide to form zinc hydroxide and ammonium nitrate, magnesium chloride with ammonium hydroxide to form magnesium hydroxide and ammonium chloride, etc. All the precipitates have different colours, textures, and solubilities when excess ammonium hydroxide solutions are added.

FAQs

Q.1. What happens when ammonium salt is treated with \({\text{NaOH}}\)?
Ans. When ammonium salt is treated with an alkali like \({\text{NaOH}}\), on heating it, ammonia gas will be released. The reaction mechanism followed in this reaction is: Hydrogen atoms of ammonium ion is positively charged. Therefore, electrons of the oxygen atom present in the hydroxyl ion attack that hydrogen atom. Then, one \({\text{N – H}}\) bond is broken and that electrons go towards the nitrogen atom which leads to the formation of an ammonia molecule. Finally, the broken hydrogen atom is taken up by oxygen atom which forms new \({\text{O – H}}\) bond to form a water \(\left( {{{\text{H}}_2}{\text{O}}} \right)\) molecule.

\({\text{N}}{{\text{H}}_4}{\text{Cl}}\,{\text{ + }}\,{\text{NaOH}}\, \to \,{\text{N}}{{\text{H}}_3}\, + \,{{\text{H}}_2}{\text{O}}\,{\text{ + NaCl}}\)

Q.2. Which salt solution does not react with ammonium hydroxide?
Ans. Calcium salt solution does not react with ammonium hydroxide. Calcium ions \({\text{C}}{{\text{a}}^{2 + }}\) does not react with ammonium hydroxide as ammonium hydroxide is a weak base, thus on ionization it forms low concentration of \({\text{O}}{{\text{H}}^{ – \,\,}}\) ions. Due to the lower concentration of \({\text{O}}{{\text{H}}^{ – \,\,}}\) ions from the ionisation of \({\text{N}}{{\text{H}}_4}{\text{OH}}\), it cannot react with calcium salt to form the precipitate of calcium hydroxide.

Q.3. Which salt solutions on reaction with an excess amount of ammonium hydroxide solution gives a deep blue solution?
Ans. Copper salt solution on reaction with excess of ammonium hydroxide solution gives a deep blue solution. When ammonium hydroxide solution is added to the solution of copper sulphate, it reacts with ammonium hydroxide to form a pale-blue precipitate of copper hydroxide along with ammonium sulphate. When an excess of ammonium hydroxide is added to this precipitate, copper hydroxide is soluble and form deep blue solution.

\({\text{CuS}}{{\text{O}}_4}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}}\, \to \,{\text{Cu}}{\left( {{\text{OH}}} \right)_2} \downarrow \, + \,{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\).

On adding excess of ammonium hydroxide, copper hydroxide gets dissolved and form a deep blue coloured solution:

\({\text{Cu}}{\left( {{\text{OH}}} \right)_2}\, + \,{\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4}\, + \,2{\text{N}}{{\text{H}}_4}{\text{OH}} \to {\left[ {{\text{Cu}}\left( {{\text{N}}{{\text{H}}_3}} \right)} \right]_4}{\text{S}}{{\text{O}}_4}\, + 4{{\text{H}}_2}{\text{O}}\)

Q.4. When an excess of ammonium hydroxide is added to calcium salts?
Ans. No reaction occurs when ammonium hydroxide is added to calcium salts even in excess amounts.

Q.5. What happens when the base reacts with ammonium salt?
Ans. Ammonia salt is heated with a base to release ammonia gas readily that can be easily detected through its smell.

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