$\mathrm{E}^{\mathrm{s}}$ of Cu is +0.34 V while that of Zn is $-$0.76 V . Explain.
$E^{\mathrm{s}}$ value of Cu is positive because of the fact that sum of sublimation enthalpy and ionisation enthalpy to convert $\mathrm{Cu}(\mathrm{s})$ to $\mathrm{Cu}^{2+}(\mathrm{aq})$ is so high that it is not compensate by its hydration enthalpy. $E^{\circ}$ value for Zn is negative because of the fact that after removal of electrons from 4 s orbital, stable $3 d^{10}$ configuration is obtained.
The halides of transition elements become more covalent with increasing oxidation state of the metal. Why?
As the oxidation state increases, size of the ion of transition element decreases. As per Fajan's rule, as the size of metal ion decreases, covalent character of the bond formed increases.
Therefore, the halide of transition elements become more covalent with increasing oxidation state of the metal.
While filling up of electrons in the atomic orbitals, the 4 s orbital is filled before the 3d orbital but reverse happens during the ionisation of the atom. Explain why?
During filling up of electrons follow $(n+l)$ rule. Here $4 s$ has lower energy than $3 d$ orbital. After the orbitals are filled 4 s goes beyond $3 d$, i.e., $4 s$ is farther from nucleus than $3 d$. So, electron from $4 s$ is removed earlier than from $3 d$.
Reactivity of transition elements decreases almost regularly from Se to Cu . Explain.
Reactivity of transition elements depends mostly upon their ionisation enthalpies. As we move from left to right in the periodic table ( Se to Cu ), ionisation enthalpies increase almost regularly. Hence, their reactivity decreases almost regularly from Se to Cu .
Match the catalysts given in Column I with the process given in Column II.
| Column I (Catalyst) |
Column II (Process) |
||
|---|---|---|---|
| A. | Ni in the presence of hydrogen | 1. | Ziegler-Natta catalyst |
| B. | $\mathrm{Cu_2Cl_2}$ |
2. | Contact process |
| C. | $\mathrm{V_2O5}$ | 3. | Vegetable oil to ghee |
| D. | Finely divided iron | 4. | Sandmeyer reaction |
| E. | $\mathrm{TiCl_4+Al(CH_3)_3}$ | 5. | Haber's process |
| 6. | Decomposition of $\mathrm{KClO_3}$ |
A. $\rightarrow(3)$ B. $\rightarrow$ (4) C. $\rightarrow$ (2) D. $\rightarrow(5)$ E. $\rightarrow(1)$
| (Catalyst) | (Process) | ||
|---|---|---|---|
| A. | Ni in the presence of hydrogen | 1. | Vegetable oil to ghee |
| B. | $\mathrm{Cu_2Cl_2}$ |
2. | Sandmeyer reaction |
| C. | $\mathrm{V_2O5}$ | 3. | Contact process $\mathrm{SO}_2 \xrightarrow{\mathrm{~V}_2 \mathrm{O}_5} \mathrm{SO}_3$ |
| D. | Finely divided iron | 4. | Haber's process $\mathrm{N}_2+3 \mathrm{H}_2 \xrightarrow{\mathrm{Fe}} 2 \mathrm{NH}_3$ |
| E. | $\mathrm{TiCl_4+Al(CH_3)_3}$ | 5. | Ziegler-Natra catalyst |