How are metals used as semiconductors refined? What is the principle of the method used like germanium, silicon etc?
Metals of high grade like germanium, silicon etc., used as semiconductors are refined by zone refining method.
Principle This method is based upon the principle that impurities are more soluble in molten state of metal than in solid state.
Write down the reactions taking place in blast furnace related to the metallurgy of iron in the temperature range 500-800 K.
Chemical reactions occurring in blast furnace related to the metallurgy of iron in the temperature range $500-800 \mathrm{~K}$ are
(i) $3 \mathrm{Fe}_2 \mathrm{O}_3+\mathrm{CO} \longrightarrow 2 \mathrm{Fe}_3 \mathrm{O}_4+\mathrm{CO}_2$
(ii) $\mathrm{Fe}_3 \mathrm{O}_4+4 \mathrm{CO} \longrightarrow 3 \mathrm{Fe}+4 \mathrm{CO}_2$
(iii) $\mathrm{Fe}_2 \mathrm{O}_3+\mathrm{CO} \longrightarrow 2 \mathrm{FeO}+\mathrm{CO}_2^2$
Give two requirements for vapour phase refining.
Two requirements for vapour phase refining are
(i) The metal should form a volatile compound with an available reagent.
(ii) The volatile compound should be easily recovered by decomposition.
Write the chemical reactions involved in the extraction of gold by cyanide process. Also give the role of zinc in the extraction.
(i) $4 \mathrm{Au}(\mathrm{s})+8 \mathrm{CN}^{-}(a q)+2 \mathrm{H}_2 \mathrm{O}(a q)+\mathrm{O}_2(g) \longrightarrow 4\left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}(a q)+4 \mathrm{OH}^{-}(a q)$
(ii) $2\left[\mathrm{Au}(\mathrm{CN})_2\right]^{-}(a q)+\mathrm{Zn}(\mathrm{s}) \longrightarrow 2 \mathrm{Au}(\mathrm{s})+\left[\mathrm{Zn}(\mathrm{CN})_4\right]^{2-}(a q)$
Zinc acts as a reducing agent in this reaction.
Match the items of Column I with items of Column II and assign the correct code.
| Column I | Column II | ||
|---|---|---|---|
| A. | Pendulum | 1. | Chrome steel |
| B. | Malachite | 2. | Nickel steel |
| C. | Calamine | 3. | $\mathrm{Na_3AlF_6}$ |
| D. | Cryolite | 4. | $\mathrm{CuCO_3.Cu(OH)_2}$ |
| 5. | $\mathrm{ZnCO_3}$ |