Question

In the reaction : $28{N{O}_3}^{-}+3A{s}_2{S}_3+4H_{2}O\to 6{As{O}_4}^{3-}+28NO+9{S{O}_4}^{2-}+8H^{+}$, Equivalent weight of $A{s}_2{S}_3$ (with molecular weight M) is :

• A. $\frac{M}{2}$
• B. $\frac{M}{4}$
• C. $\frac{M}{24}$
• D. $\frac{M}{28}$

Answer 1

The correct option is B $\frac{M}{4}$

The oxidation number of arsenic in $A{s}_2{S}_3$ and in ${As{O}_4}^{3-}$ is +3 and +5.
The change in oxidation number per As atom $=5-3=2$.
The change in oxidation number of 2 As atoms $=2\times 2=4.$
The equivalent mass of $A{s}_2{S}_3=\frac{FormulamassofA{s}_2{S}_3}{TotalchangeinoxidationnumberofAs}=\frac{M}{4}$