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10 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
10 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
10 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.
New answer posted
10 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
New answer posted
10 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
10 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.
New answer posted
10 months agoContributor-Level 10
35. Option (ii) 8 is correct since in face centred cubic unit cell the number of atoms per unit cell is 4 atoms and hence the number of tetrahedral voids in fcc unit cell is found to be 8
New answer posted
10 months agoContributor-Level 10
14. The considerations during the extraction of metals by electrochemical method are :
a) Reactivity of metals: If the metals are reactive and are likely to react with water then the metals should be isolated by the electrolysis of their purified molten ore rather than their aqueous solution.
b) Suitability of electrodes:The electrode is carefully chosen so that they should not react with the product of electrolysis. If they react then the electrodes must be made of a material which is quite cheap so their replacement should not increase the cost of the process.
New answer posted
10 months agoContributor-Level 10
34. Option (iv) 5 is correct since silicon is doped with a pentavalent substance like Phosphorus or Arsenic so, four out of five electrons are used in the formation of four covalent bonds with four of its neighbouring silicon atoms. The fifth electron is extra and becomes delocalised. These delocalised electrons increase the conductivity of doped silicon.
New answer posted
10 months agoContributor-Level 10
13. Vapor phase refining or Van Arkel's method is used for refining Zr and Ti.
Vapor refining or vapor phase process: The metal is collected in the form of volatile compound that decomposes to pure metal.
Van Arkel method: This method is useful for removing all Oxygen and nitrogen present in the form of impurity in metals like Zr and Ti. The crude metal is heated in an empty vessel with a small amount of iodine. The metal iodine being more covalent volatilises. Impure Zr reacts with iodine to form zirconium tera iodide.
The following reaction occurs Zr + 2I2? ZrI4 The metal iodide is decomposed on
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