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Chemistry · 2026 · 3 marks
CBSE 2026 · Region 1 · Set 1 · Q23
(a) Answer the following: (i) Why is the Equilibrium Constant ( K_c ) related to E_cell^° and not to E_cell? (ii) Two metals 'A' and 'B' have…
Answer the following :
(i)
Why is the Equilibrium Constant $\displaystyle \left(\mathrm{K}_{\mathrm{c}}\right)$ related to $\displaystyle \mathrm{E}_{\text {cell }}^{\circ}$ and not to $\displaystyle \mathrm{E}_{\text {cell }}$ ?
(ii)
Two metals 'A' and 'B' have standard electrode potential values of -$\displaystyle 0.24$ V and +$\displaystyle 0.80$ V respectively. Which of these will liberate hydrogen gas from dil. $\displaystyle \mathrm{H}_{2} \mathrm{SO}_{4}$ ?
(iii)
Write the cell reaction which occurs in lead storage battery when it is in charging.
What type of battery is Mercury cell ? Why it is more advantageous than dry cell ? Write overall reaction taking place in Mercury cell.
Marking-scheme solution
(a)
.
(i)
Because at equilibrium , Ecell = $\displaystyle 0$
(ii)
Metal ‘A’
(iii)
2PbSO4(s)+ 2H2O(l) → PbO2(s) + Pb(s) + 2H2SO4(aq)
OR
$\displaystyle 23$(b).
• Mercury cell – Primary cell
• It provides constant potential difference throughout its life.
• Zn(Hg) + HgO(s) → ZnO(s) + Hg (l)
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.