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 $\mathrm{I}_2$.
$$\mathrm{Zr}+2 \mathrm{I}_2 \xrightarrow{870 \mathrm{~K}} \mathrm{ZrI}_4 \xrightarrow{2075 \mathrm{~K}} \mathrm{Zr}+2 \mathrm{I}_2$$
Although carbon and hydrogen are better reducing agents but they are not used to reduce metallic oxides at high temperatures. Why?
Because at high temperatures, carbon and hydrogen react with metals to form carbides and hydrides respectively. So, carbon and hydrogen are not better reducing agents to reduce metallic oxide.
How do we separate two sulphide ores by froth floatation method? Explain with an example.
Two sulphide ores can be separated by adjusting the proportion of oil and water or by using depressants, e.g., if an ore contains ZnS and PbS both, a depressant NaCN is added during froth floatation. It forms a complex with ZnS and prevents it from coming into froth. PbS comes into the froth and thus separated.