A) 0.395V
B) 0.495V
C) 0.240 V
D) 0.595 V
Correct Answer: A
Solution :
Idea This problem includes concept of equilibrium constant and nemst equation. Students are advised to go through step by step determination of concentration and then cell emf using nernst equation. Nernst equation for given cell reaction may be written as \[E_{cell}^{{}^\circ }=\frac{0.059}{2}\log \frac{[{{H}^{+}}]_{RHS}^{2}{{[P{{H}_{2}}]}_{LHS}}}{[{{H}^{+}}]_{LHS}^{2}{{[P{{H}_{2}}]}_{RHS}}}\] \[\alpha <<1\] \[[O{{H}^{-}}]=\sqrt{{{k}_{b}}\times C}\] \[[O{{H}^{-}}]=\sqrt{{{10}^{-5}}\times {{10}^{-1}}}={{10}^{-3}}\] \[{{[{{H}^{+}}]}_{LHS}}={{10}^{-11}}\] \[[{{H}^{+}}][O{{H}^{-}}]={{10}^{-14}}[{{H}^{+}}]={{10}^{-11}}\] \[{{[{{H}^{+}}]}_{RHS}}=\sqrt{{{K}_{a}}\times C}=\sqrt{{{10}^{-7}}\times {{10}^{-1}}}={{10}^{-4}}\] \[E_{cell}^{{}^\circ }=\frac{0.059}{2}\log \frac{{{({{10}^{-4}})}^{2}}\times 0.1}{{{({{10}^{-11}})}^{2}}}\times 1=0.395\,\,\text{V}\] TEST Edge In general, the questions based on nernst equation are asked frequently, so students are advised to study the nernst equation for various types of cell and emf calculation. The question related to end and spontaniety of reaction may also be asked. \[\Delta h=-nFE_{cell}^{{}^\circ }\] \[\therefore \] Positive value of \[E_{cell}^{{}^\circ }\] show spontaneous reaction.
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