1. Explain the following :

(a) CO₂ is a better reducing agent below 710 K whereas CO is a better reducing agent above 710 K.

(b) Generally, sulfide ores are converted into oxides before reduction.

(c) Silica is added to the sulfide ore of copper in the reverberatory furnace.

(d) Carbon and hydrogen are not used as reducing agents at high temperatures.

(e) Vapor phase refining method is used for the purification of Ti.

 $\frac{dE}{dT}$ is the temperature Co-efficient of cell. The cell having less variation of EMF, with respect to temperature have high efficiency.

Below 1350° C, Mg can reduce Al₂O₃ and above 1350°C, Al can reduce MgO (from Ellingham diagram).

Melting and boiling point of Mg are lower than that of Al.

In ores/mineral available earthy and undesired impurities are gangue

Sol. Reactivity towards ${\mathrm{A}\mathrm{g}\mathrm{N}\mathrm{O}}_3$  depend on stability of carbocation formed

Leaching involves the given reaction,

$4Au\left(s\right)+8C{N}^{-}\left(aq\right)+2H_{2}O\left(aq\right)+O_2\left(g\right)\to 4{\left[Au{\left(CN\right)}_2\right]}^{-}\left(aq\right)+4O{H}^{-}\left(aq\right)$              

Here, O₂ is required for formation of Au (l) cyanide complex but no complex in absence of O₂.

$2{\left[Au{\left(CN\right)}_2\right]}^{-}\left(aq\right)+Zn\left(s\right)\to {\left[Zn{\left(CN\right)}_4\right]}^{2-}\left(aq\right)+2Au\left(s\right)$                

In above displacement reaction, Zn is oxidized.