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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.

Silver ores and native gold have to be leached with metal cyanides as these form water soluble complexes with sodium or potassium cyanide.

{Ag}_{2} S + 4 NaCN \to \underset{Soluble complex}{2 Na [Ag (CN)_{2}]} + {Na}_{2} S 8 Au + 8 NaCN + 2 H_{2} O \to \underset{Soluble complex}{4 Na [Au (CN)_{2}]} + 4 NaOH

From this silver can be precipitated by addition of more electropositive metal like Zn.

2Na[Ag(CN)₂] + Zn → 2Ag ↓ + Na₂ Zn(CN)₄2Na[Au(CN)₂] + Zn → 2Au↓ + Na₂ Zn(CN)₄

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.

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