The choice of a reducing agent in a particular case depends on thermodynamic factor. How far do you agree with this statement? Support your opinion with two examples.

Carbon monoxide is more effective agent that carbon below 983 K but above this temperature the reverse is true. How would you explain this?

The value of Δ_rG° for formation of Cr₂O₃ is – 540 kJmol^–1 and that of Al₂O₃ is – 827 kJ mol^-1. Is the reduction of Cr₂O₃ possible with Al?

Predict the modes of occurrence of the following three types of metals:

(i) Highly reactive (e.g., Na)
(ii) Moderately reactive (e.g., Fe)
(iii) Noble metal (e.g., Au)

How do non-metals occur in nature? How are they extracted/isolated from their natural resources?

Name the chief ores of tin, iron and aluminium. What methods are employed for the concentration/purification of their ores?

Name three ores which are concentrated by froth-floatation process. What is meant by depressant?

78.

Why is it advantageous to roast a sulphide ore to the oxide before reduction?

Discuss some of the factors which need consideration before deciding on the method of extraction of metal from its ore.

You are provided with samples of some impure metals such as zinc, copper and germanium. Which methods could you recommend for the purification of each of these metals?