Why is an external emf of more than 2.2 V required for the extraction of $\mathrm{Cl}_2$ from brine?
$$2 \mathrm{Cl}^{-}(a q)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow 2 \mathrm{OH}^{-}(a q)+\mathrm{H}_2(g)+\mathrm{Cl}_2(g)$$
For the given reaction, value of $\Delta G^{\circ}$ is +422 kJ.
Using $\Delta G^{\circ}=-n F E^{\circ}$, the value of $E^{\circ}=-2.2 \mathrm{~V}$.
Therefore, an external emf greater than 2.2 V is required for the extraction of $\mathrm{Cl}_2$ from brine.
At temperature above 1073 K, coke can be used to reduce Fe 0 to Fe . How can you justify this reduction with Ellingham diagram?
Using Ellingham diagram, we observe that at temperature greater than 1073 K ; $\Delta G_{(\mathrm{C}, \mathrm{CO})}<\Delta G_{(\mathrm{Fe}, \mathrm{FeO})}$. We know that according to Ellingham diagram, compound having lower $\Delta_f G^s$ undergo its formation. Hence, coke can reduce FeO to Fe .
Wrought iron is the purest form of iron. Write a reaction used for the preparation of wrought iron from cast iron. How can the impurities of sulphur, silicon and phosphorus be removed from cast iron?
(a) $\underset{\begin{array}{c}\text { Hematite } \\ \text { lining }\end{array}}{\mathrm{Fe}_2 \mathrm{O}_3}+\underset{\begin{array}{c}\text { Impurities } \\ \text { (present in cast iron) }\end{array}}{3 \mathrm{C}} \longrightarrow \underset{\substack{\text { Wrought } \\ \text { iron }}}{2 \mathrm{Fe}}+3 \mathrm{CO}$
This reaction takes place in reverberatory furnace lined with haematite.
(b) The haematite oxidises S to $\mathrm{SO}_2$, Si to $\mathrm{SiO}_2$ and P to $\mathrm{P}_4 \mathrm{O}_{10}$. Sometimes limestone is added as flux. Impurities of $\mathrm{S}, \mathrm{Si}$ and P oxidise and pass into slag. The metal is removed and freed from slag by passing through rollers.
How is copper extracted from low grade copper ores?
Copper is extracted from low grade copper ore using hydrometallurgy method. For this purpose, ore is leached out using bacteria. The solution containing $\mathrm{Cu}^{2+}$ is treated with scrap iron and $\mathrm{H}_2$.
$$\mathrm{Cu}^{2+}(a q)+\mathrm{H}_2(g) \longrightarrow \mathrm{Cu}(s)+2 \mathrm{H}^{+}(a q)$$
Write two basic requirements for refining of a metal by Mond's process and by van Arkel Method.
Two basic requirements are
(i) Metal should form volatile compound with available reagent.
(ii) The volatile compound should be easily decomposable so that it can be recovered easily.
(a) Mond's process includes conversion of Ni to $\mathrm{Ni}(\mathrm{CO})_4$ and then decomposition of $\mathrm{Ni}(\mathrm{CO})_4$ to Ni.
$$\begin{gathered} \mathrm{Ni}+4 \mathrm{CO} \longrightarrow \mathrm{Ni}(\mathrm{CO})_4 \\ \mathrm{Ni}(\mathrm{CO})_4 \xrightarrow{450-470 \mathrm{~K}} \mathrm{Ni}+4 \mathrm{CO} \end{gathered}$$
(b) van Arkel method includes conversion of Zr to volatile $\mathrm{ZrI}_4$ and then decomposition of $\mathrm{ZrI}_4$ to Zr and $\mathrm{I}_2$.
$$\mathrm{Zr}+2 \mathrm{I}_2 \xrightarrow{870 \mathrm{~K}} \mathrm{ZrI}_4 \xrightarrow{2075 \mathrm{~K}} \mathrm{Zr}+2 \mathrm{I}_2$$