Electrochemistry · Chemistry · Class 12

A voltaic cell is made by connecting two half cells represented by half equations below:

$$\begin{aligned} & \mathrm{Sn}_{(a q)}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Sn}_{(\mathrm{s})} \mathrm{E}^{\mathrm{o}}=-0.14 \mathrm{~V} \\ & \mathrm{Fe}^{3+}{ }_{(\mathrm{aq})}+\mathrm{e}^{-} \rightarrow \mathrm{Fe}^{2+}{ }_{(\mathrm{aq})} \mathrm{E}^{\mathrm{o}}=+0.77 \mathrm{~V} \end{aligned}$$

Which statement is correct about this voltaic cell?

Four half reactions I to IV are shown below:

I. $$2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_2+2 \mathrm{e}^{-}$$

II. $$4 \mathrm{OH}^{-} \rightarrow \mathrm{O}_2+2 \mathrm{H}_2 \mathrm{O}+2 \mathrm{e}^{-}$$

III. $$\mathrm{Na}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{Na}$$

IV. $$2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_2$$

Which two of these reactions are most likely to occur when concentrated brine is electrolysed?

Which of the following cell was used in Apollo space programme?

(a) (i) What should be the signs (positive/ negative) for $$\mathrm{E}_{\text {Cell }}^0$$ and $$\Delta \mathrm{G}^0$$ for a spontaneous redox reaction occurring under standard conditions?

(ii) State Faraday's first law of electrolysis.

OR

(b) Calculate the emf of the following cell at $$298 \mathrm{~K}$$ :

$$\begin{aligned} & \mathrm{Fe}_{(\mathrm{s})}\left|\mathrm{Fe}^{2+}(0.01 \mathrm{M}) \| \mathrm{H}_{(1 \mathrm{M})}^{+}\right| \mathrm{H}_{2(\mathrm{~g})}(1 \mathrm{bar}), \mathrm{Pt}_{(\mathrm{s})} \\ & \text { Given } \mathrm{E}_{\mathrm{Cen}}^0=0.44 \mathrm{~V}. \end{aligned}$$

Rahul set-up an experiment to find resistance of aqueous $$\mathrm{KCl}$$ solution for different concentrations at $$298 \mathrm{~K}$$ using a conductivity cell connected to a Wheatstone bridge. He fed the Wheatstone bridge with a.c. power in the audio frequency range 550 to 5000 cycles per second. Once the resistance was calculated from null point he also calculated the conductivity $$K$$ and molar conductivity $$\wedge_m$$ and recorded his readings in tabular form.

Answer the following questions:

(a) Why does conductivity decrease with dilution?

(b) If $$\wedge_{\mathrm{m}}{ }^0$$ of $$\mathrm{KCl}$$ is $$150.0 \mathrm{~S} \mathrm{~cm} \mathrm{~mol}^{-1}$$, calculate the degree of dissociation of $$0.01 \mathrm{M} \mathrm{KCl}$$.

(c) If Rahul had used $$\mathrm{HCl}$$ instead to $$\mathrm{KCl}$$ then would you except the $$\wedge_{\mathrm{m}}$$ values to be more or less than those per $$\mathrm{KCl}$$ for a given concentration. Justify.

OR

(c) Amit, a classmate of Rahul repeated the same experiment with $$\mathrm{CH}_3 \mathrm{COOH}$$ solution instead of $$\mathrm{KCl}$$ solution. Give one point that would be similar and one that would be different in his observations as compared to Rahul.