Chapter 7

$$ \text { Write equations for the electrolysis of } \mathrm{CaH}_{2} \text { in fused state. } $$

A metal is known to form fluoride \(M \mathrm{~F}_{2}\). When 10 ampere electricity is passed throwgh i multen salt for \(330 \mathrm{sec}, 1.95 \mathrm{~g}\) metal is deposited. Find out the atomic weight of metal. What will be the quantity of charge required to deposit the same mass of \(\mathrm{Cu}\) from \(\mathrm{CuSO}_{4}\) (aq.) (At. wt. of \(\mathrm{Cu}=63.6\) )

Write the nernst equation and e.m.f. of the following cells at \(298 \mathrm{~K}\) : (a) \(\mathrm{Mg}(\mathrm{s})\left|\mathrm{Mg}^{2+}(0.001 \mathrm{M}) \| \mathrm{Cu}^{2+}(0.0001 \mathrm{M})\right| \mathrm{Cu}(\mathrm{s})\) (b) \(\mathrm{Fe}(\mathrm{s})\left|\mathrm{Fe}^{2+}(0.001 M) \| \mathrm{H}^{\mathrm{i}}(1 \mathrm{M})\right| \mathrm{H}_{2}(\mathrm{~g})(1 \mathrm{bar}) \mid \mathrm{Pt}(\mathrm{s})\) (c) \(\mathrm{Sn}(\mathrm{s})\left|\mathrm{Sn}^{2+}(0.050 \mathrm{M}) \| \mathrm{H}^{+}(0.020 \mathrm{M})\right| \mathrm{H}_{2}(\mathrm{~g})(1 \mathrm{bar}) \mid \mathrm{Pt}(\mathrm{s})\) (d) \(\mathrm{Pt}(\mathrm{s})\left|\mathrm{Br}_{2}(\mathrm{l})\right| \mathrm{Br}^{-}(0.010 \mathrm{M}) \| \mathrm{H}^{+}(0.030 \mathrm{M}) \mid \mathrm{H}_{2}(\mathrm{~g})(\mathrm{I} \mathrm{bar}) ! \mathrm{Pt}(\mathrm{s})\) Given : \(E_{\text {OP }}^{\circ} \mathrm{Mg}=2.36 \mathrm{~V}, E_{\mathrm{OP}}^{\circ} \mathrm{Cu}=-0.34 \mathrm{~V}, E_{\mathrm{OP}}^{\mathrm{O}} \mathrm{Fe}=0.44 \mathrm{~V}\) \(E_{\mathrm{OP}}^{\circ} \mathrm{Sn}=0.14 \mathrm{~V}\) and \(E_{\mathrm{OP}}^{\circ} \mathrm{Br}_{2}=-1.09 \mathrm{~V}\) respectively.

For the cell : $$ \text { Zn }\left|\begin{array}{c} \mathrm{Zn}_{\text {aq }}^{2+} \\ 1 M \end{array}\right|\left|\begin{array}{c|c} \mathrm{Cu}_{a q}^{2+} \\ 2 M \end{array}\right| \mathrm{Cu} $$ Calculate the values for ; (a) cell reaction, (b) \(E_{\text {cell }}^{\circ}\). (c) \(E_{\text {cell }}\) (d) the minimum concentration of \(\mathrm{Cu}^{2+}\) at which cell reaction is spontaneous if \(\mathrm{Zn}^{2+}\) is \(1 M\) (e) does the displacement of \(\mathrm{Cu}^{2+}\) goes almost to completion. Given : \(E_{R P_{\mathrm{Cu}^{2+} / \mathrm{Cu}}}^{\circ}=+0.35 \mathrm{~V}\) $$ E_{R P_{\mathrm{Zn}^{2+} / Z n}}^{\circ}=-0.76 \mathrm{~V} $$

The e.m.f. of a cell corresponding to the reaction : $$ \begin{aligned} \mathrm{Zn}(s)+2 \mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Zn}^{2+}+& \mathrm{H}_{2}(\mathrm{~g}) \\ (0.1 \mathrm{M}) &(1 \mathrm{~atm}) \end{aligned} $$ is \(0.28 \mathrm{~V}\) at \(25^{\circ} \mathrm{C}\) and \(E_{\mathrm{Zn} / \mathrm{Zn}^{2+}}^{\circ}=0.76 \mathrm{~V}\) (i) Write half cell reactions. (ii) Calculate \(\mathrm{pH}\) of the solution at \(\mathrm{H}\) electrode.

$$ \begin{aligned} &\text { The e.m.f. of the cell } M \mid M^{n+}(0.02 M) \| \mathrm{H}^{+}(1 M) \mathrm{H}_{2(\mathrm{~g})}(1 \mathrm{~atm}) \mathrm{Pt} \text { at }\\\ &25^{\circ} \mathrm{C} \text { is } 0.81 \mathrm{~V} \text { . Calculate the valence of metal if } E^{\circ}{ }_{\ldots 1 / 2}^{n+}=0.76 \mathrm{~V} \end{aligned} $$

Given the standard electrode potentials; \(\mathrm{K}^{+} / \mathrm{K}=-2.93 \mathrm{~V}, \quad \mathrm{Ag}^{+} / \mathrm{Ag}=0.80 \mathrm{~V}, \quad \mathrm{Hg}^{2+} / \mathrm{Hg}=0.79 \mathrm{~V}\) \(\mathrm{Mg}^{2+} / \mathrm{Mg}=-2.37 \mathrm{~V}, \quad \mathrm{Cr}^{3+} / \mathrm{Cr}=-0.74 \mathrm{~V}\) Arrange these metals in their increasing order of reducing power.

Two metals \(A\) and \(B\) have \(E_{\mathrm{RP}}^{\circ}=+0.76 \mathrm{~V}\) and \(-0.80 \mathrm{~V}\) respectively. Which will liberate \(\mathrm{H}_{2}\) from \(\mathrm{H}_{2} \mathrm{SO}_{4} ?\)

Calculate the standard cell potentials of galvanic cell in which the following reactions take place : (Given \(E_{\text {OP }}^{\circ} \mathrm{Cr}, \mathrm{Cd}, \mathrm{Fe}^{2+}, \mathrm{Ag}\) are \(0.74 \mathrm{~V}, 0.40 \mathrm{~V},-0.77 \mathrm{~V}\) and \(-0.80 \mathrm{~V}\) respectively) (a) \(2 \mathrm{Cr}_{(\mathrm{s})}+3 \mathrm{Cd}^{2+}\) (aq.) \(\longrightarrow 2 \mathrm{Cr}^{3+}{ }_{\text {(aq. })}^{3+} 3 \mathrm{Cd}\) (b) \(\mathrm{Fe}^{2+}{ }_{\text {(aq.) }}+\mathrm{Ag}_{(\mathrm{aq})}^{+} \longrightarrow \mathrm{Fe}^{3+}{ }_{\text {(aq.) }}+\mathrm{Ag}_{(\mathrm{s})}\) Calculate the \(\Delta_{\mathrm{r}} G^{\circ}\) and equilibrium constant of the reactions.