Question

How many ions per molecule are produced in the solution when Mohr salt is dissolved in excess of water?
A. 4
B. 5
C. 6
D. 10

Answer 1

Hint: Mohr salt is a double salt, and with the chemical name ammonium iron (II) sulphate. It consists of two ions mainly i.e. ferrous ions, and ammonium ions. By writing the chemical formula of Mohr salt, the no. of ions dissolved could be known.

Complete step by step answer:
First, we will know about the Mohr salt (green transparent crystals). It is a very common reagent used in the labs, as it can be easily crystallized.
As we know, ferrous sulphate salts dissolves in water, like that ferrous ammonium sulphate salt i.e. Mohr salt too dissolves in water, and gives the aqua complex with the octahedral geometry.
If it depicts octahedral geometry then we can say that the 6 water molecules, or ligands are attached to the ferrous.
Now, the chemical formula of ferrous ammonium sulphate is FeSO$_4$.(NH$_4$)$_2$SO$_4$.6H$_2$O.
Thus, Mohr salt undergoes the complete dissociation, on dissolving into the aqueous solution.
So, we can say that it is prepared by dissolving the mixture of hydrated ferrous, and ammonium sulphate in the presence of an acid, and further proceeds with the crystallisation.
In the last, we can conclude that the 6 ions per molecule are produced, when it is dissolved in excess water. The correct option is (C).

Note: There is no need of confusion why we call Mohr salt a double salt, because it consists of two simple salts i.e. ferrous sulphate, and the ammonium sulphate. Remember while preparing the Mohr salt, the mixture should be equimolar in amount, as it is a hazardous substance.