Question

A cell diagram shown in the figure contains one litre of buffer solution of $HA(p{K}_a=4)$ and $NaA$ in both compartment. What is the cell e.m.f?

• A. $0.03V$
• B. $0.06V$
• C. $-0.06V$
• D. None of these

Answer 1

Answer: (B)

$0.06V$

$E_{cell}=\frac{0.06}{1}log\frac{[H^{+}{]}_{RHS}}{[H^{+}{]}_{LHS}}$
or $E_{cell}=0.06\left[\right(pH{)}_{LHS}-\left(pH{)}_{RHS}\right]$
$(pH{)}_{LHS}=p{K}_a+log\frac{\left[A^{-}\right]}{\left[HA\right]}$
$=4+log\left(\frac{1}{0.1}\right)=5;(pH{)}_{RHS}=4$
$E_{cell}=0.06(5-4)=+0.06V$ {Option (B)}