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General Principles And Processes of Isolation Of Elements

Long Answer Type

81.

Name the chief forms of the occurrence of the following in the earth crust:
(a) aluminium, (b) calcium, (c) sodium, (d) lead.

135 Views

Short Answer Type

82.

Sodium metal cannot be obtained by the electrolysis of aqueous sodium chloride solution.

137 Views

83.

Write the chemical reactions involved in the extraction of metallic silver from argentite.

177 Views

84. Why is Fe an abundant element on earth, and why are the elements with higher atomic numbers increasingly rare?

116 Views

85.

Silver ores and native gold have to be leached with metal cyanides. Suggest a reason for this.

205 Views

Long Answer Type

86.
Describe the principle of froth floatations process. What is the role of stabilizer and of a depressant? Give one example of each.

Froth floatation process: This process is based on the fact that the sulphide ore particles are only moistened with oil, whereas oxide and gangue particles are moistened by water. For this, the powdered ore is mixed with water and a little pine oil and whole mixture is then stirred vigorously through rotating paddle by blowing compressed air. The oil forms a foam or froth with air. The ore particles stick to the froth and rises to the surface, while gangue are left in water. The froth is skimmed off, collected and allowed to subside to get concentrated ore. This is especially suitable for sulphide ores.

Fig. Froth floatation process.

(a) Role of stabilizer: Stabilizers are used to stabilize the froth. Examples: Cresols and aniline.

(b) Role of depressant: Depressants are used to prevent certain type of particles from forming the froth with bubbles.
Examples: NaCN can be used as a depressant in the separation of ZnS and PbS ore.

947 Views

Short Answer Type

87. Explain hydrometallurgy.

193 Views

88.

Differentiate between 'minerals' and 'ores'.

167 Views

Long Answer Type

89.

State briefly the principles which serve as basis for the following operations in metallurgy:
(i) Froth floation process.
(ii) Zone refinnting.
(iii) Refining by liquation.

758 Views

90.

What chemical principle is involved in choosing a reducing agent for gettting the metal from its oxide ore? Consider the metal oxides, Al₂O₃ and Fe₂O₃ and justify the choice of reducing agent in each case.

787 Views