JEE MAIN - Chemistry (2025 - 7th April Morning Shift - No. 12)
Given below are two statements :
Statement I : Mohr's salt is composed of only three types of ions-ferrous, ammonium and sulfate.
Statement II : If the molar conductance at infinite dilution for ferrous, ammonium and sulfate ions are $x_1, x_2$ and $x_3 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}$, respectively then the molar conductance for Mohr's salt solution at infinite dilution would be given by $x_1+x_2+2 x_3$
In the light of the given statements, choose the correct answer from the options given below :
Explanation
Mohr's salt is chemically represented as $ \mathrm{FeSO}_4 \cdot\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4 \cdot 6 \mathrm{H}_2 \mathrm{O} $.
To understand its composition, Mohr's salt dissociates into the following ions:
Fe$^ {2+} $ (ferrous ion)
2 NH$_4^+ $ (ammonium ions)
2 SO$_4^{2-} $ (sulfate ions)
Thus, Mohr's salt contains ferrous, ammonium, and sulfate ions, but also has water molecules that hydrate these ions.
Using Kohlrausch's Law of independent ionic mobility, the molar conductance at infinite dilution for an electrolyte is the sum of the ionic conductances of its constituent ions:
$ \lambda_{\mathrm{m}}^{\infty}(\text{Mohr's salt}) = \mathrm{x}_1 + 2\mathrm{x}_2 + 2\mathrm{x}_3 $
Here:
$ x_1 $ represents the molar conductance of the ferrous ion (Fe$^ {2+} $),
$ x_2 $ represents the molar conductance of the ammonium ion (NH$_4^+$),
$ x_3 $ represents the molar conductance of the sulfate ion (SO$_4^{2-}$).
Therefore, statement II should include the correct expression $ x_1 + 2x_2 + 2x_3 $ to accurately describe the molar conductance for Mohr's salt.
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