JEE Questions for Chemistry General Principles And Processes Of Isolation Of Elements Quiz 2 - MCQExams.com

Refining of a metal (such as copper ) by electrolysis , the crude metal used as  the anode going into solution and the pure metal being  deposited upon the cathode called electrolytic refining .

Tin is obtained by reducing the ore cassiterite with coal in a reverberatory furnace ; lime stone is added to produce a slag with impurities, which can be removed.

SnO₂  +  2C → sn + 2 CO.

Crude tin so obtained is contaminated with iron, lead and other metals. It is therefore, remelted on an inclined furnace. The process is called liquation. The easily fusible tin metals away and the less fusible impurities are left behind. Molten tin is finally stirred with green poles of wood in contact with air. In this process any remaining metal impurities are oxidized forming a scum, which rises to the surface and is removed. This process is called poling.

In the electrolytic refining of zinc

Anode → impure zinc

Cathode → strip of pure zinc

Electrolyte → acidified zinc sulphate solution

At anode → Oxidation of metal

                     (i.e., Zn → Zn²⁺ + 2e^–)

                            (impure)

At cathode → reduction of metal ions

                       (i.e., Zn²⁺ + 2e^– → Zn)

                          (Form solution)    (pure)

The purest zinc is obtained by zone refining . This method is particularly used when metals are required in high degree of purity. It is based on the principle that when an impure metal in a molten state is allowed to cool, only the metal crystallizes while the impurities remain present in the molten state or melt.

Azurite is one of the basic copper (11) carbonate minerals, the other being bright green malachite. Simple copper carbonate (CuCO₃) is not known to exist in nature. Azurite has the formula Cu(CO₃)₂(OH)₂ with the copper (11) cations linked to two different anions, carbonate and hydroxide.

Hence the composition of azurite mineral is 2CuCO₃.Cu (OH)_2.

The chemical formula of malachite is Cu₂CO₃(OH)₂. Hence the composition is CuCO₃.Cu(OH)_2.

Aluminium is obtained from mining the mineral bauxite which is mainly aluminium oxide (Al₂O₃) and bauxite must be purified prior to electrolysis, adding to the manufacturing costs. The purified bauxite ore of aluminium oxide is continuously fed in. The mineral cryolite is added to lower the boiling point and dissolve the ore. So the electrolyte is a mixture of molten aluminium oxide and cryolite minerals.

In the process of electrorefining of copper, Copper dissolves from the anode and goes into the electrolyte and an equivalent amount of copper from the electrolyte gets deposited on the cathode. The insoluble impurities containing less reactive metals such as silver and gold fall to the bottom of the electrolyte cell in the form of anode mud. The more reactive metals such as iron dissolves in the solution and remain in the solution itself.

Silver is extracted from the ore-argentite (Ag₂S). The process of extraction of silver is called as cyanide process as sodium cyanide solution is used. The ore is crushed, concentrated and then treated with sodium cyanide solution.This reaction forms sodium argento cyanide Na[Ag(CN)₂].

2 Ag₂S + 4 NaCN + O₂ → 2 Na[Ag(CN)₂] + Na₂S + SO₂

The solution of sodium argento cyanide combines with zinc dust and forms sodium tetra cyanozicate and precipitated silver. This precipitated silver is called spongy silver.

Zn  + 2 Na[Ag(CN)₂] → Na₂[Zn(CN)₄] + 2 Ag ↓

The spongy silver is fused with potassium nitrate to btain pure silver. Then the silver obtained is purified by electrolytic process.

During roasting of pyrite ore, following reaction will occurs.

2FeS + 3O₂→ 2FeO + 2SO₂↑

Hence this reaction does not take place during the smelting process of extraction.

Highly reactive element Na is extracted by electrolysis of fused salts.

In blast furnace, Fe₂O₃ is reduced to Fe by CO.

Fe₂O₃ + 3CO → 2Fe + 3CO₂ ↑

Caliche is crude chile salt petre (NaNO₃) which contains iodine as sodium iodate, NaIO₃ impurity.

Cyanide process is used for the extraction of Au, floatation process uses pine oil as a foaming agent, electrolytic reduction is used in the extraction of Al and zone refining process produces ultra pure Ge.

Gallium arsenide is purified by zone refining method.

Metallic ore contain gangue particles like sand, clay, quartz, and during extraction by pyrometallurgy, zinc blende is subjected to roasting to remove impurities.