General Principles of Isolation of Elements Test - 7

The salt which is least likely to be found in minerals is nitrate because nitrates occur naturally in plants and are manufactured endogenously in the bodies of animals. They are added as fertilisers to the soil.

This is based on the differences between gravities of the ore and the gangue particles. Therefore, it is a type of gravity separation. In one such process, an upward stream of running water is used to wash the powdered ore. The lighter gangue particles are washed away and the heavier ores are left behind.

Boron and Indium (of high purity) used in semi-conductors are purified by zone refining process. Zone melting (or zone refining or floating zone process) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal (in practice, the crystal is pulled through the heater). The molten region melts impure solid at its forward edge and leaves a wake of purer material solidified behind it as it moves through the ingot. The impurities concentrate in the melt, and are moved to one end of the ingot.

Froth flotation process is used for the concentration of sulphide ores. Galena is a sulphide ore of lead (PbS), and it is concentrated by froth flotation process.

Metals more reactive than iron can be used for the reduction of Fe₂O₃ in the thermite process.
Except barium, all the other given metals can be used as reducing agents in Goldschmidt thermite process. However, aluminium is the more commonly used metal.

Ores of gold and silver are concentrated by chemical leaching method.

Silver is extracted from the ore argentite (Ag₂S). The process of extraction of silver is called 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].

Ag₂S + 4NaCN ⇌ 2Na[Ag(CN)₂] + Na₂S
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 + 2Na[Ag(CN)₂] → Na2[Zn(CN)₄] + 2Ag

Decomposition of limestone on heating, in the absence of air, is called calcination.

The slag is lighter and has lower melting point than the metal.

As ΔG^o_f for most of the sulphides are more than those of CS₂ and H₂S so carbon and hydrogen can not reduce metal sulphides into metal.