The cell may be represented as:
Pt(H21 atm)|H+(1 M)||Ag+(salt)|Ag(s)
E∘cell=E∘Ag+/Ag−E∘H+/H2
=0.799−0=0.799 V
Given, emf of the cell =0.711 V
H2+2Ag+→2Ag+2H+
Q=[Ag]2[H+]2[H2][Ag+]2=12×121×[Ag+]2=1[Ag+]2
Applying Nernst equation,
E=E∘−0.0591nlog10Q
or 0.711=0.799−0.05912log101[Ag+]2
[Ag+]=0.03243 mol L−1
Ag2SO3⇌2Ag+0.03243+SO2−40.016215
Ksp[Ag+]2[SO2−4]=(0.03243)2×(0.016215)=1.705×10−2.