CBSE 2026 · Region 2 · Set 1 · Q32 · 5 marks
(a)The conductivity of $\displaystyle 0.1 \mathrm{~mol} \mathrm{~L}^{-1}$ solution of $\displaystyle \mathrm{NaC} l$ is $\displaystyle 1.06 \times 10^{-2} \mathrm{~S} \mathrm{~cm}^{-1}$. Calculate its molar conductivity and degree of dissociation. $\displaystyle 3$ + $\displaystyle 2$ \[\begin{aligned} & \lambda^{\circ} \mathrm{Na}^{+}=50.1 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} \\ & \lambda^{\circ}{ }_{\mathrm{Cl}}^{-}=76.5 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} \end{aligned} \](b)(i)Following cell reaction occurs in a galvanic cell : \[2 \mathrm{Ag}_{(\mathrm{aq})}^{+}+\mathrm{Zn}_{(\mathrm{s})} \longrightarrow 2 \mathrm{Ag}_{(\mathrm{s})}+\mathrm{Zn}_{(\mathrm{aq})}^{2+} \mathrm{E}_{(\mathrm{cell})}^{\circ}=+1.56 \mathrm{~V} \] Predict the direction of flow of current.(ii)Differentiate between a primary battery and a secondary battery.(a)Resistance of a conductivity cell filled with $\displaystyle 0.1$ M KCl solution is $\displaystyle 100 \Omega$. If the resistance of the same cell when filled with $\displaystyle 0.01$ $\displaystyle \mathrm{mol} \mathrm{L}^{-1} \mathrm{KC} l$ solution is $\displaystyle 300 \Omega$, calculate the conductivity and molar conductivity of $\displaystyle 0.01 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{KCl}$ solution. The conductivity of $\displaystyle 0.1 \mathrm{M} \mathrm{KC} l$ solution is $\displaystyle 1.29 \times 10^{-2} \mathrm{~S} \mathrm{~cm}^{-1}$. $\displaystyle 3$ + $\displaystyle 2$(b)(i)Write any two advantages of $\displaystyle \mathrm{H}_{2}-\mathrm{O}_{2}$ fuel cell.(ii)Why does the cell potential of mercury cell remain constant throughout the life ?
(a)
The conductivity of $\displaystyle 0.1 \mathrm{~mol} \mathrm{~L}^{-1}$ solution of $\displaystyle \mathrm{NaC} l$ is $\displaystyle 1.06 \times 10^{-2} \mathrm{~S} \mathrm{~cm}^{-1}$. Calculate its molar conductivity and degree of dissociation. $\displaystyle 3$ + $\displaystyle 2$ \[\begin{aligned} & \lambda^{\circ} \mathrm{Na}^{+}=50.1 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} \\ & \lambda^{\circ}{ }_{\mathrm{Cl}}^{-}=76.5 \mathrm{~S} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} \end{aligned} \]
(b)(i)
Following cell reaction occurs in a galvanic cell : \[2 \mathrm{Ag}_{(\mathrm{aq})}^{+}+\mathrm{Zn}_{(\mathrm{s})} \longrightarrow 2 \mathrm{Ag}_{(\mathrm{s})}+\mathrm{Zn}_{(\mathrm{aq})}^{2+} \mathrm{E}_{(\mathrm{cell})}^{\circ}=+1.56 \mathrm{~V} \] Predict the direction of flow of current.
(ii)
Differentiate between a primary battery and a secondary battery.
(a)
Resistance of a conductivity cell filled with $\displaystyle 0.1$ M KCl solution is $\displaystyle 100 \Omega$. If the resistance of the same cell when filled with $\displaystyle 0.01$ $\displaystyle \mathrm{mol} \mathrm{L}^{-1} \mathrm{KC} l$ solution is $\displaystyle 300 \Omega$, calculate the conductivity and molar conductivity of $\displaystyle 0.01 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{KCl}$ solution. The conductivity of $\displaystyle 0.1 \mathrm{M} \mathrm{KC} l$ solution is $\displaystyle 1.29 \times 10^{-2} \mathrm{~S} \mathrm{~cm}^{-1}$. $\displaystyle 3$ + $\displaystyle 2$
(b)(i)
Write any two advantages of $\displaystyle \mathrm{H}_{2}-\mathrm{O}_{2}$ fuel cell.
(ii)
Why does the cell potential of mercury cell remain constant throughout the life ?
Marking-scheme solution
(A)
.
(a)
•°NaCl = $\displaystyle 50.1$ + $\displaystyle 76.5$ = $\displaystyle 126.6$ Scm2 mol−$\displaystyle 1$
𝛬𝑚=
k X $\displaystyle 1000$
𝑀
=
$\displaystyle 1.06$ X $\displaystyle 10$−$\displaystyle 2$ X $\displaystyle 1000$
= $\displaystyle 106$ Scm2 mol−$\displaystyle 1$
α=
𝛬𝑚
𝛬𝑚
α=
$\displaystyle 126.6$ = $\displaystyle 0.8372$ or $\displaystyle 83.72$ %
(i)
Current will flow from Silver to Zinc /cathode to anode
(ii)
Primary battery – the reaction occurs only once, it cannot be reused again.
Secondary battery – It can be recharged and can be used again.
$\displaystyle 32$(B).
(a)
k =
𝑅(
𝑙
𝐴)
𝑙
𝐴)= k R
= $\displaystyle 1.29$ x $\displaystyle 10$-$\displaystyle 2$ x $\displaystyle 100$
=$\displaystyle 1.29$ cm-$\displaystyle 1$
k =
$\displaystyle 1$ 𝑋 $\displaystyle 1.29$
=$\displaystyle 0.0043$ Scm-$\displaystyle 1$
𝛬𝑚=
k X $\displaystyle 1000$
𝑀
= $\displaystyle 0.0043$ X $\displaystyle 1000$
=$\displaystyle 430$ Scm2mol-$\displaystyle 1$
(b)(i)
1. Fuel cells are pollution free.
2. High efficiency.
(ii)
The cell potential remains constant during its life as the overall reaction
does not involve any ion in solution whose concentration can change in
its life time.
ElectrochemistryConductance of Electrolytic SolutionsApplylong_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.