Name the chief forms of the occurrence of the following in the earth crust:
(a) aluminium, (b) calcium, (c) sodium, (d) lead.
Sodium metal cannot be obtained by the electrolysis of aqueous sodium chloride solution.
Write the chemical reactions involved in the extraction of metallic silver from argentite.
Silver ores and native gold have to be leached with metal cyanides. Suggest a reason for this.
Describe the principle of froth floatations process. What is the role of stabilizer and of a depressant? Give one example of each.
This method is based on the fact that more electropositive metal can displace less electropositive metal from its salt solution. The concentrated ore is bleached with aqueous solution of suitable reagent (NaCN solution of Cl2in the presence of water) to extract the metal salt in complex salts solution in water. The salt solution is then either electrolyzed or precipitated by adding more electropositive metal. This method also known as complex salt formation method.
Ag2S +4NaCN → 2Na[Ag(CN)2] +Na2S
2Na[Ag(CN)2] +Zn → 2Ag +Na2[Zn(CN)4]
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.
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.