CBSE 2024 · Region 3 · Set 1 · Q31 · 5 marks
(i)Calculate emf of the following cell at $\displaystyle 25$°C : \[\mathrm{Zn}(\mathrm{~s})\left|\mathrm{Zn}^{2+}(0 \cdot 001 \mathrm{M})\right|\left|\mathrm{Cd}^{2+}(0 \cdot 1 \mathrm{M})\right| \mathrm{Cd}(\mathrm{~s}) \] Given : $\displaystyle \mathrm{E}_{\mathrm{Zn}^{2+} / \mathrm{Zn}}^{\mathrm{o}}=-0.76 \mathrm{~V}, \mathrm{E}_{\mathrm{Cd}^{2+} / \mathrm{Cd}}^{\mathrm{o}}=-0.40 \mathrm{~V}[\log 10=1]$(ii)State Faraday's second law of electrolysis. How will the pH of aqueous NaCl solution be affected when it is electrolysed ?(i)Calculate the $\displaystyle \Delta_{\mathrm{r}} \mathrm{G}^{0}$ and $\displaystyle \log \mathrm{K}_{\mathrm{c}}$ for the following cell reaction : \[\mathrm{Fe}(\mathrm{~s})+\mathrm{Ag}^{+}(\mathrm{aq}) \rightleftharpoons \mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{Ag}(\mathrm{~s}) \] Given : $\displaystyle \mathrm{E}_{\mathrm{Fe}^{2+} / \mathrm{Fe}}^{\mathrm{o}}=-0.44 \mathrm{~V}, \mathrm{E}_{\mathrm{Ag}^{+} / \mathrm{Ag}}^{\mathrm{o}}=+0.80 \mathrm{~V}$, \[1 \mathrm{~F}=96500 \mathrm{C} \mathrm{~mol}^{-1} \](ii)Write any two advantages of the fuel cells over primary and secondary batteries ?(iii)How many Faradays are required for the oxidation of $\displaystyle 1$ mole of $\displaystyle \mathrm{H}_{2} \mathrm{O}$ to $\displaystyle \mathrm{O}_{2}$ ?
(i)
Calculate emf of the following cell at $\displaystyle 25$°C : \[\mathrm{Zn}(\mathrm{~s})\left|\mathrm{Zn}^{2+}(0 \cdot 001 \mathrm{M})\right|\left|\mathrm{Cd}^{2+}(0 \cdot 1 \mathrm{M})\right| \mathrm{Cd}(\mathrm{~s}) \] Given : $\displaystyle \mathrm{E}_{\mathrm{Zn}^{2+} / \mathrm{Zn}}^{\mathrm{o}}=-0.76 \mathrm{~V}, \mathrm{E}_{\mathrm{Cd}^{2+} / \mathrm{Cd}}^{\mathrm{o}}=-0.40 \mathrm{~V}[\log 10=1]$
(ii)
State Faraday's second law of electrolysis. How will the pH of aqueous NaCl solution be affected when it is electrolysed ?
(i)
Calculate the $\displaystyle \Delta_{\mathrm{r}} \mathrm{G}^{0}$ and $\displaystyle \log \mathrm{K}_{\mathrm{c}}$ for the following cell reaction : \[\mathrm{Fe}(\mathrm{~s})+\mathrm{Ag}^{+}(\mathrm{aq}) \rightleftharpoons \mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{Ag}(\mathrm{~s}) \] Given : $\displaystyle \mathrm{E}_{\mathrm{Fe}^{2+} / \mathrm{Fe}}^{\mathrm{o}}=-0.44 \mathrm{~V}, \mathrm{E}_{\mathrm{Ag}^{+} / \mathrm{Ag}}^{\mathrm{o}}=+0.80 \mathrm{~V}$, \[1 \mathrm{~F}=96500 \mathrm{C} \mathrm{~mol}^{-1} \]
(ii)
Write any two advantages of the fuel cells over primary and secondary batteries ?
(iii)
How many Faradays are required for the oxidation of $\displaystyle 1$ mole of $\displaystyle \mathrm{H}_{2} \mathrm{O}$ to $\displaystyle \mathrm{O}_{2}$ ?
Marking-scheme solution
(i)
E°cell = E°cathode -E°anode
\[=-0.40-(-0.76) \mathrm{V}
\]
= 0.36V
\[\mathrm{E}_{\text {cell }}=\mathrm{E}^{\circ} \text { Cell }-\frac{0.059}{2} \log \frac{\left[\mathrm{Zn}^{2+}\right]}{\left[\mathrm{Cd}^{2+}\right]}
\]
ElectrochemistryNernst EquationApplylong_answerhard
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CBSE Class 12 Chemistry past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.