General Principles of Isolation of Elements Test - 4

This process is also called auto reduction process or air reduction process. The sulphide ores of less electropositive metals like Hg, Pb, Cu, etc. are heated in air so as to convert part of the ore into oxide or sulphate, which then reacts with the remaining sulphide ore to give the metal and sulphur dioxide. No external reducing agent is used in this process.

Silicon, manganese and carbon are removed through oxidation of molten pig iron during Bessemer process and the product obtained after removal of such impurities is called steel.

Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered as a mixture of metal oxides and silicon dioxide. So, CaSiO₃ is known as slag.

This is wrong as red bauxite also contains some silica.

Pure alumina melts at about 2000°C and is a bad conductor of electricity. If alumina is dissolved and fused cryolite is added to it, the mixture melts at 900°C and becomes a good conductor of electricity.

Duralumin is made up of aluminium, copper, manganese and magnesium, and is used in aircraft construction.

Copper-nickel alloy is called constantan. It is used in electrical work for its high resistance.
Alloy of nickel and chromium is called chromel.
Manganin is an alloy of copper, manganese and nickel.
Copper, nickel and zinc form an alloy called German silver.

Highly reactive metals are extracted by the electrolysis of their molten chlorides or oxides.
For example, when molten sodium chloride is electrolysed, sodium metal is obtained on cathode and chlorine gas is obtained at anode.
2Na⁺ + 2e^- → 2Na
2Cl^- - 2e → Cl₂

The electrolytic method is the most suitable method for refining the non-ferrous metals. A large number of metals, e.g. copper, silver, gold, nickel, etc, are refined by this method. In an electrolytic cell, the impure metal is made anode and a thin strip of pure metal is made cathode. A solution of a suitable salt of the concerned metal is used to fill the electrolytic cell. On passing electricity, the anode undergoes dissolution, while the pure metal gets deposited at the cathode. Insoluble impurities fall below the anode in the form of anode mud.

In this method, the ore is treated chemically with a suitable reagent that preferentially dissolves the active component of the ore. The concentrated ore form is then recovered from the solution by a suitable chemical method. A typical example of ore concentration by leaching process is the purification of bauxite using NaOH solution as a leachant. Bauxite is digested with concentrated solution of caustic soda at 150°C in an autoclave. Aluminium oxide dissolves in NaOH leaving behind the insoluble impurities, which are removed by filtration.