Question

Equivalent weight of Mohr salt is $1$ .Justify.

Answer 1

Hint : Mohr’s Salt is called ammonium iron (II) sulphate. It is an inorganic compound whose chemical formula is represented as ${(N{H_4})_2}Fe{(S{O_4})_2}{({H_2}O)_6}$ .It contains two primary cations, ammonium cation ( $NH_4^ +$ ) and ferrous cation ( $F{e^{2 + }}$ ). At STP, Mohr’s salt exists as a crystalline solid that is bluish-green in colour.
Equivalent weight =$\dfrac{\text{Molecular weight}}{\text{ Valency factor}}$.

Complete Step By Step Answer:
Mohr’s salt is known to belong to a family of double sulphates which are collectively called Tutton’s salts. All members of Mohr’s salt are known to form crystals with a monoclinic geometry. The bonding patterns in the molecular structure of Mohr’s salt feature octahedral centres made up of ${[Fe{({H_2}O)_6}]^{2 + }}$ centres. These centres are known to form hydrogen bonds with the ammonium and sulphate ions.
The oxidation state of iron varies from $+ 3$ to $+ 2$ .
Hence, valency factor is $3 - 2 = 1$ The valency factor is the change in the oxidation state of $Fe$ .
Molecular weight $= 392$
Using the above formula, we can calculate the equivalent weight:
Equivalent weight $=\dfrac{\text{molecular weight}}{\text{Valency factor}}$
Equivalent weight $= \dfrac{{392}}{1}$
Equivalent weight $= 392$
Hence, the equivalent weight of Mohr’s salt is $392$ .

Additional Information:
In the field of analytical chemistry, Mohr’s salt is used as a source of $F{e^{2 + }}$ ions. There is an advantage of using Mohr’s salt as a source of ferrous ions that it has a relatively long shelf life and is also resistant to oxidation due to atmospheric exposure. Mohr’s salt is also used in Fricke’s dosimeter because it helps measure high doses of gamma radiation.

Note :
The equivalent weight of any substance is equal to the mass of the substance in grams that would react with or replace one gram of hydrogen. It is expressed as the ratio of molecular weight to valence.