The d- and f- Block Elements Test

Directions For Questions

Transition metal and their compounds are used as catalysts in industry and in biological system. For example, in the contact process, vanadium compounds in the +5 state ($$V_2O_5$$ or $$VO_3{^-}$$) are used to oxidise $$SO_2$$ to $$SO_3$$ : $$SO_2$$ + $$\displaystyle{\frac{1}{2}}O_2 \overset{V_2O_5} {\rightarrow}$$ $$SO_3$$. It is thought that the actual oxidation process takes place in two stages. In the first step, $$V^{5+}$$ in the presence of oxide ions converts $$SO_2$$ to $$SO_3$$. At the same time, $$V^{5+}$$ is reduced to $$V^{4+}$$. $$2V^{5+} + O^{2-} + SO_2 \rightarrow 2V^{4+} + SO_3$$. In the second step, $$V^{5+}$$ is regenerated from $$V^{4+}$$ by oxygen : $$2V^{4+} + \displaystyle{\frac{1}{2}O_2 \rightarrow} 2V^{5+} + O^{2-}$$. The overall process is, of course, the sum of these two steps: $$SO_2 + \displaystyle{\frac{1}{2}}O_2 \rightarrow SO_3$$.

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