Question

To precipitate group iii cations $N{H_4}Cl$ should be added to the solution before the addition of ammonium hydroxide. Explain why.

Answer 1

Hint: Ammonium hydroxide is the solution of ammonia in water. It is a colourless liquid which has a molar mass of 35.04 grams per moles. It has a pungent odour that of fish and has the standard enthalpy of formation equal to 80 kilojoules per mole. Its solubility decreases on increasing the temperature of water solvent.

Complete step by step answer:
To answer this question we must know the qualitative analysis is different group anions and cations.
Qualitative analysis of metal ions in solution.
 It is important to know how we detect the presence of specific ions in an aqueous solution.
This is called the qualitative analysis which falls in the category of analytical chemistry
Generally answers the question of what can be present in a sample.
The underlying principle on which the qualitative analysis of metal ions work is that iron will undergo a specific chemical reaction with some specific region which will give a product which is observable in nature.
First, we add reagents that explore the general properties of the iron to separate them into groups of ions. Now after separating them into major groups be or separate them into subgroups with the reaction that will distinguish left general properties. The third step is to add reagent that will specifically confirm if the individual ions are present.
The question says, to precipitate group Iii cations $N{H_4}Cl$ should be added to the solution before the addition of ammonium hydroxide.
From a basic solution of hydrogen sulphide, the ions of group 3 are precipitated either as sulphides or their hydroxides.
To ensure the precipitation to occur mostly we must take care that the solution of hydrogen sulphide is not too basic because if the concentration of Hydroxide ion is high unwanted precipitation of magnesium Hydroxide can take place. In order to make sure the necessary concentration of hydroxide we add an Ammonia Ammonium Chloride buffer. This buffer is obtained by adding Ammonia to a solution of Ammonium Chloride.
Hence to precipitate group iii cations $N{H_4}Cl$ should be added to the solution before the addition of ammonium hydroxide.

Note: Ammonium hydroxide is used in the formation of the organic and inorganic chemicals which contain nitrogen. It helps in formation of chloramine which is considered as a good disinfectant. It helps in manufacturing of chemical fertilizers. It helps in the furniture darkening.