Which of the following statements are correct?
In the extraction of chlorine from brine ........... .
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.