Answer

The standard electrode potential of $\mathrm{Mg}^{2+} \mid \mathrm{Mg}$ can be measured with respect to the standard hydrogen electrode, represented by $\mathrm{Pt_(s)}, \mathrm{H_2(g)}(1 \mathrm{~atm}) \mid \mathrm{H_(a q)}^{+}(1 \mathrm{M})$.

A cell, consisting of $\mathrm{Mg} \mid \mathrm{MgSO_4}(\mathrm{aq} 1 \mathrm{M})$ as the anode and the standard hydrogen electrode as the cathode, is set up.

$$ \mathrm{Mg}\left|\mathrm{Mg}^{2+}(\mathrm{aq}, 1 \mathrm{M}) \| \mathrm{H}^{+}(\mathrm{aq}, 1 \mathrm{M})\right| \mathrm{H_2}(\mathrm{~g}, 1 \text { bar }), \mathrm{Pt_{(s)}} $$

Then, the emf of the cell is measured and this measured emf is the standard electrode potential of the magnesium electrode.

$E^{\ominus}=E_{R}^{\ominus}-E_{L}^{\ominus}$

Here, $E_{R}^{\ominus}$ for the standard hydrogen electrode is zero.

$$ \begin{aligned} & \therefore E^{\ominus}=0-E_{L}^{\ominus} \\ & =-E_{L}^{\ominus} \end{aligned} $$

Answer

Zinc is more reactive than copper. Therefore, zinc can displace copper from its salt solution. If copper sulphate solution is stored in a zinc pot, then zinc will displace copper from the copper sulphate solution.

$\mathrm{Zn}+\mathrm{CuSO_4} \longrightarrow \mathrm{ZnSO_4}+\mathrm{Cu}$

Hence, copper sulphate solution cannot be stored in a zinc pot.

Answer

Substances that are stronger oxidising agents than ferrous ions can oxidise ferrous ions.

$\mathrm{Fe}^{2+} \longrightarrow \mathrm{Fe}^{3+}+\mathrm{e}^{-1} ; E^{\ominus}=-0.77 \mathrm{~V}$

This implies that the substances having higher reduction potentials than

$+0.77 \mathrm{~V}$ can oxidise ferrous ions to ferric ions. Three substances that can do so are $\mathrm{F_2}, \mathrm{Cl_2}$, and $\mathrm{O_2}$.