Electrochemistry PYQ — Physical Chemistry Exams

For \(\mathrm{C{r_2}O_7^{2 - } + 14{H^ + } + 6{e^ - }\buildrel {Yields} \over \longrightarrow 2C{r^{3 + }} + 7{H_2}O,{E^\Upsilon } = 1.33}\) V at \([C{r_2}O_7^{2 - }] = 4.5\) millimole, \([C{r^{3 + }}] = 1.5\) millimole and \(E = 1.067\) V, then calculate the pH of the solution.

Find the emf of the following cell reaction. Given, \(E_{\mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}}^{\Upsilon}=-0.72 \mathrm{~V}\) and \(E_{\mathrm{Fe}^{2+} / \mathrm{Fe}}^{\Upsilon}= -0.42 \mathrm{~V}\) at \(25^{\circ} \mathrm{C}\) is \(\mathrm{Cr}\left|\mathrm{Cr}^{3+}(0.1 \mathrm{M})\right| \mid \mathrm{Fe}^{2+} (0.1 \mathrm{M}) \mid \mathrm{Fe}\)

At \(291 \mathrm{~K}\), saturated solution of \(\mathrm{BaSO}_4\) was found to have a specific conductivity of \(3.648 \times 10^{-6} \mathrm{ohm}^{-1} \mathrm{~cm}^{-1}\) and that of water being used is \(1.25 \times 10^{-6} \mathrm{ohm}^{-1} \mathrm{~cm}^{-1}\). If the ionic conductances of \(\mathrm{Ba}^{2+}\) and \(\mathrm{SO}_4^{2-}\) are 110 and \(136.6 \mathrm{ohm}^{-1} \mathrm{~cm}^2 \mathrm{~mol}^{-1}\) respectively. The solubility of \(\mathrm{BaSO}_4\) at \(291 \mathrm{~K}\) will be [Atomic masses of \(\mathrm{Ba}=137, \mathrm{~S}=32, \mathrm{O}=16]\)

Assertion (A) Sodium acetate on Kolbe’s electrolysis gives ethane.

Reason (R) Methyl free radical is formed at cathode.

When a current of 10 A is passes through molten AlCl\(_3\) for 1.608 minutes. The mass of Al deposited will be

[Atomic mass of Al = 27 g]

The molar conductivities \(\left(\lambda_{\mathrm{m}}^{\Upsilon}\right)\) at infinite dilution of \(\mathrm{KBr}, \mathrm{HBr}\) and \(\mathrm{KNH}_2\) are 120.5, 420.6 and \(90.48 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^{-1}\) respectively. Find the value of \(\lambda_{\mathrm{m}}^\Upsilon\) for \(\mathrm{NH}_3\).

In the electrolysis of a CuSO\(_4\) solution, how many grames of Cu are plated out on the cathode, in the time that is required to liberate 5.6 L of O\(_2\)(g), measured at 1 atm and 273 K, at the anode?

If hydrogen electrons dipped in two solutions of pH = 3 and pH = 6 are connected by a salt bridge, the emf of the resulting cell is

38.6 amperes of current is passed for 100 seconds through an aqueous \(\mathrm{CuSO}_4\) solution using platinum electrodes. The mass of copper consumed from the solution and volume of gas liberated at STP are respectively (molar mass of \(\mathrm{Cu}=63.54 \mathrm{~g} \mathrm{~mol}^{-1}\)).

The reduction potential of hydrogen electrode at \(25^{\circ} \mathrm{C}\) in a neutral solution is (\(p_{\mathrm{H}_2}=1\) bar)

96.5 amperes current is passed through the molten \(\mathrm{AlCl}_3\) for 100 seconds. The mass of aluminium deposited at the cathode is (atomic weight of \(\mathrm{Al}=27 \mathrm{u}\))

The $E^{-}$of $M\left|M^{2+} \| \mathrm{Cu}^{2+}\right| \mathrm{Cu}$ is 0.3 V .

At what concentration of $\mathrm{Cu}^{2+}\left(\mathrm{in} \mathrm{mol} \mathrm{L} \mathrm{L}^{-1}\right)$, the $\mathrm{E}_{\mathrm{cel}}$ value becomes zero ? $\left(\frac{2.303 R T}{F}=0.06\right)$

(Conc. of $\mathrm{M}^{2+}=0.1 \mathrm{M}$ )

The standard reduction potentials of $2 \mathrm{H}^{+} / \mathrm{H}_2, \mathrm{Cu}^{2+} / \mathrm{Cu}, \mathrm{Zn}^{2+} / \mathrm{Zn}$ and $\mathrm{NO}_3^{-}, \mathrm{H}^{-} / \mathrm{NO}$ are 0.0 , +0.34 . -0.76 and 0.97 V respectively. Observe the following reactions

I. $\mathrm{Zn}+\mathrm{HCI} \rightarrow$

II. $\mathrm{Cu}+\mathrm{HCl} \rightarrow$

III. $\mathrm{Cu}+\mathrm{HNO}_3 \rightarrow$

Which reactions does not liberate $\mathrm{H}_2(g)$ ?

Aqueous $\mathrm{CuSO}_4$ solution was electrolysed by passing 2 amp of current for 10 min . What is the weight (in g) of copper deposited at cathode ?

$$\left(\mathrm{Cu}=63 \mathrm{u} ; F=96500 \mathrm{C} \mathrm{~mol}^{-1}\right)$$

The standard reduction potentials of $2 \mathrm{H}^{+} / \mathrm{H}_2, \mathrm{Cu}^{2+} / \mathrm{Cu}, \mathrm{Zn}^{2+} / \mathrm{Zn}$ and $\mathrm{NO}_3^{-}, \mathrm{H}^{-} / \mathrm{NO}$ are 0.0 0.34 . -0.76 and 0.97 V respectively. Identify the correct statements from the following.

I. $\mathrm{H}^{+}$does not oxidise Cu to $\mathrm{Cu}^{2+}$

II. Zn reduces $\mathrm{Cu}^{2+}$ to Cu

III. $\mathrm{NO}_3^{-}$oxidises Cu to $\mathrm{Cu}^{2+}$

Consider the following standard electrode potentials ( $E^{\circ}$ in volts) in aqueous solution.

$$\begin{array}{|c|c|c|} \hline \text { Element } & M^{3+} / M & M^{+} / M \\ \hline \mathrm{Al} & -1.66 & +0.55 \\ \hline \mathrm{TI} & +1.26 & -0.34 \\ \hline \end{array}$$

Based on this data. which of the following statements is correct?

Consider the cell reaction at 300 K .

$$A(s)+B^{2+}(a q) \rightleftharpoons A^{2+}(a q)+B(s)$$

Its $E^{\ominus}$ is 1.0 V . The $\Delta_r H^{\ominus}$ of the reaction is $-163 \mathrm{kJmol}^{-1}$.

What is $\Delta_r s^{\ominus}$ (in $\mathrm{JK}^{-1}$ ) of the reaction?

$$\left(F=96500 \mathrm{C} \mathrm{~mol}^{-1}\right)$$