Chemistry NCERT Exemplar Solutions Class 12th Chapter Six
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4 months agoContributor-Level 10
24. Option (ii)
Purification of metal crystals by making a thin region of crystal undergo melting is known as Zone refining. The molten crystal is then moved up along the crystal to get pure form of it. This process is used to get pure form of Silicon and Germanium. Basic principle of the zone refining process is that the impurities are more soluble in molten metal than solid metal to get pure form of metal.
New answer posted
4 months agoContributor-Level 10
23. Option (i)
Explanation: Aluminum is the third most abundant metal in the earth's crust (8.3 percent approximately by weight). It is found in a variety of igneous minerals, including mica and clays. The second most abundant metal in the earth's crust is iron.
New answer posted
4 months agoContributor-Level 10
22. Option (iv)
Copper (I) oxide is reduced by copper (I) sulfide in this reaction. Because copper is reduced by itself in this process, it is referred to as auto reduction.
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4 months agoContributor-Level 10
21. Option (iii)
Copper ore is mixed with silica before heating in a reverberatory furnace. When heated in a reverberatory furnace, the iron oxide slags of iron silicate and copper are produced. This product is produced in the form of copper matte in the furnace. Presence of Cu2S and FeS is observed in copper matte. In these compounds, we observe the sulfides of Copper (I) Cu2+ and Iron (II) Fe2+.
New answer posted
4 months agoContributor-Level 10
20. Option (i)
Explanation: 2H2O + Cl−→2OH− + H2 + Cl2
The ΔG? is +422 kJ for this reaction. We get ΔE? = −2.2 V, when we convert it to ΔE? (using G? = E? F). It will, of course, require an external e.m.f. greater than 2.2 V. However, electrolysis necessitates an excess potential in order to overcome some other impeding reactions. Thus, Cl2 is obtained through electrolysis, which produces H2 and aqueous NaOH as byproducts. In addition, molten NaCl is electrolyzed. However, in that case, Na metal is formed rat
New answer posted
4 months agoContributor-Level 10
19. The metal gold is a nonreactive metal. It is found as a native metal in its free state.
So, it is not compulsory to separate it by a chemical process. Thus, gold is leached to get it in its pure form. In the metallurgy of gold (Au), the respective metal is leached with a dilute mixture of NaCN or KCN in the presence of air where Gold (Au) is oxidized by oxygen of the air to Au+cation which then merges with ions to form a soluble compound.
4Au (s)+8CN− (aq)+O2− (g)+2H2O− (aq)→4 [Au (CN)2]− (aq)+4OH− (aq)
Gold is then obtained from this soluble compound x by replacement method by using a much more electropositive Z
New answer posted
4 months agoContributor-Level 10
18. The two import requirements for performing the Vapor Phase Refining Method:
a) The metal which is to be refined should form a volatile compound with an available reagent.
b) The volatile compound formed must be easily decomposable so that it is easy to recover the desired metal.
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4 months agoContributor-Level 10
17. The chemical reactions taking place in Blast furnace in the temperature range 500-800 K are:
3Fe2O3 + CO→ 2Fe3O4 + CO2
Fe3O4 + 4CO→ 3Fe + 4CO2
Fe2O3 + CO→ 2FeO + CO2
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4 months agoContributor-Level 10
16. Semiconducting metal is produced by the zone refining method.
Zone refining is centered on the principle that the impurities which are included in the metal ores are more soluble in the molten state as compared to the solid-state of metals.
Zone refining is mostly used for obtaining semiconductor and other metals which are highly pure, e.g., germanium, silicon, etc.
New answer posted
4 months agoContributor-Level 10
15. In metallurgical processes, Flux works as various types of agents like chemical agents, cleaning/purifying agents.
Fluxes have many important properties such as corrosivity, cleanability, conductivity, volatility, etc.
Flux, when combined with gangue together, forms slag i.e. Flux + Gangue = Slag
As compared to gangue, slag separates much easily from the ore, in this way the removal of gangue also becomes much easier.
Flux is useful for making the molten mass more conducting which helps to remove impurities from metals through electrolytic metallurgical processes.
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