Electrochemistry · JEE Main previous year questions

2020 6 questions

1. Q722020 · 6 Sept 2020 · Shift 1· Numerical answer

   Potassium chlorate is prepared by the electrolysis of $\mathrm{KCl}$ in basic solution $$6O{\mathrm{H}}^{-}+\mathrm{C}{\mathrm{l}}^{-}\to \mathrm{Cl}{\mathrm{O}}_3^{-}+3{\mathrm{H}}_2\mathrm{O}+6{\mathrm{e}}^{-}$$ If only $60\%$ of the current is utilized in the reaction, the time (rounded to the nearest hour) required to produce $10\text{ g}$ of $\mathrm{KCl}{\mathrm{O}}_3$ using a current of $2\text{ A}$ is ______ . (Given : $F=96,500\mathrm{C}\mathrm{mo}{\mathrm{l}}^{-1}$; molar mass of $\mathrm{KCl}{\mathrm{O}}_3=122\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$)

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   Answer: 11

2. Q642020 · 3 Sept 2020 · Shift 1

   Let ${\mathrm{C}}_{\mathrm{NaCl}}$ and ${\mathrm{C}}_{\mathrm{BaS}{\mathrm{O}}_4}$ be the conductances (in S) measured for saturated aqueous solutions of $\mathrm{NaCl}$ and $\mathrm{BaS}{\mathrm{O}}_4$, respectively, at a temperature T. Which of the following is false?

   1. A.Ionic mobilities of ions from both salts increase with T.
   2. B.${\mathrm{C}}_{\mathrm{NaCl}}({\mathrm{T}}_2)>{\mathrm{C}}_{\mathrm{NaCl}}({\mathrm{T}}_1)$ for ${\mathrm{T}}_2>{\mathrm{T}}_1$
   3. C.${\mathrm{C}}_{\mathrm{BaS}{\mathrm{O}}_4}({\mathrm{T}}_2)>{\mathrm{C}}_{\mathrm{BaS}{\mathrm{O}}_4}({\mathrm{T}}_1)$ for ${\mathrm{T}}_2>{\mathrm{T}}_1$
   4. D.${\mathrm{C}}_{\mathrm{NaCl}}\gg {\mathrm{C}}_{\mathrm{BaS}{\mathrm{O}}_4}$ at a given T
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   Answer: D

3. Q732020 · 9 Jan 2020 · Shift 1· Numerical answer

   108 g of silver (molar mass $108{\text{ g mol}}^{-1}$) is deposited at cathode from $\mathrm{AgN}{\mathrm{O}}_3(\mathrm{aq})$ solution by a certain quantity of electricity. The volume (in L) of oxygen gas produced at 273 K and 1 bar pressure from water by the same quantity of electricity is _______.

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   Answer: 5.66 to 5.68

4. Q702020 · 9 Jan 2020 · Shift 2

   Amongst the following, the form of water with the lowest ionic conductance at 298 K is :

   1. A.saline water used for intravenous injection
   2. B.sea water
   3. C.distilled water
   4. D.water from a well
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   Answer: C

5. Q722020 · 8 Jan 2020 · Shift 1· Numerical answer

   What would be the electrode potential for the given half cell reaction at pH = 5? _______. $$2{\mathrm{H}}_2\mathrm{O}\to {\mathrm{O}}_2+4{\mathrm{H}}^{\oplus }+4e^{-};E_{\mathrm{red}}^0=1.23\text{ V}$$ $(\mathrm{R}=8.314{\text{ J mol}}^{-1}{\text{ K}}^{-1};\text{Temp}=298\text{ K}$; oxygen under std. atm. pressure of 1 bar)

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   Answer: 1.52 to 1.53

6. Q662020 · 7 Jan 2020 · Shift 1

   Given that the standard potentials $(E^{\circ })$ of $\mathrm{C}{\mathrm{u}}^{2+}/Cu$ and $\mathrm{C}{\mathrm{u}}^{+}/Cu$ are $0.34\text{ V}$ and $0.522\text{ V}$ respectively, the $E^{\circ }$ of $\mathrm{C}{\mathrm{u}}^{2+}/C{\mathrm{u}}^{+}$ :

   1. A.$-0.182\text{ V}$
   2. B.$-0.158\text{ V}$
   3. C.$0.182\text{ V}$
   4. D.$+0.158\text{ V}$
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   Answer: D