Explain the trends in $E_{{M^{3 + }}/{M^{2 + }}}^ o $ electrode potential.
The scandium has low value of $\mathrm{M}^{3+} / \mathrm{M}^{2+}$ potentials because of its noble gas configuration.
The highest value of $\mathrm{M}^{3+} / \mathrm{M}^{2+}$ is for zinc because $\mathrm{Zn}^{2+}$ has $\mathrm{d}^{10}$ configuration which is extra stable. High value of $\mathrm{Mn}^{3+} \mid \mathrm{Mn}^{2+}$ is due to half-filled $\left(d^{5}\right)$ orbitals in $\mathrm{Mn}^{2+}$ while low values of $\mathrm{Fe}^{3+} \mid \mathrm{Fe}^{2+}$ shows extra stability of $\mathrm{Fe}^{3+}\left(d^{5}\right)$. The vanadium has comparatively less negative values because of higher stability of $\mathrm{V}^{2+}$ that has half filled configuration $\left(\mathrm{t}_{2 \mathrm{~g}}^{3}\right)$.
The high value of $\mathrm{Co}^{3+} / \mathrm{Co}^{2+}$ is because of high values of $\mathrm{CFSE}$ of $\mathrm{t}_{2 \mathrm{~g}}^{5} \mathrm{e}^{2}\left[\mathrm{Co}^{2+}\right]$ system in a aqueous medium.
The high values of $\mathrm{M}^{3+} / \mathrm{M}^{2+}$ of $\mathrm{Mn}^{3+}$ and $\mathrm{Co}^{3+}$ indicates that they are good oxidizing agents while $\mathrm{Ti}^{2+}, \mathrm{V}^{2+} \mathrm{Cr}^{2+}$ etc. are good reducing agents and thus these liberates $\mathrm{H}_{2}$ from acids.
Ex. : $2 \mathrm{Cr}_{\text {(aq) }}^{2+}+2 \mathrm{H}_{\text {(aq) }}^{+} \rightarrow 2 \mathrm{Cr}_{\text {(aq) }}^{3+}+\mathrm{H}_{2 \text { (aq) }} \uparrow$
Elements | Electrode potentials$\left(\mathrm{M}^{3+} / \mathrm{M}^{2+}\right)$ |
$Ti$ | $-0.37$ |
$V$ | $-0.26$ |
$\mathrm{Cr}$ | $-0.41$ |
$Mn$ | $+1.57$ |
$\mathrm{Fe}$ | $+0.77$ |
$Co$ | $+1.97$ |
In presence of oxidizing agents such as $\mathrm{HNO}_{3}$, the chromium forms layer of oxide $\mathrm{Cr}_{2} \mathrm{O}_{3}$ on its surface and hence it is passive towards oxidation.
Which of the following compound is coloured ?
Stainless steel does not rust because
Stainless steel is an alloy of
Which one of the following characteristics of the transition metals is associated with their catalytic activity
Steel is manufactured from