d Block Elements : Silver and its Compounds

 

Silver and its Compounds 

Ores : Argentite (silver glance) Ag2S, Horn silver (AgCl), Ruby silver (Pyrargyrite) 3Ag2S. Sb2S3.

Extraction : Cyanide process  or Mac Arthus-Forrest cyanide process : This method depends on the fact that silver, its sulphide or chloride, forms soluble complex with alkali cyanides in the silver. This implies that silver compounds will dissolve in solution of alkali cyanides in the presence of blast of air.

          4Ag + 8NaCN + 2H2O + O2  \leftrightharpoons 4Na [Ag(CN)2] + 4NaOH

          4Ag + 8CN– + 2H2O + O2  \leftrightharpoons 4 [Ag(CN)2]– + 4OH–

          Or

          Ag2S + 4NaCN \leftrightharpoons 2Na [Ag(CN)2] + Na2S

          AgCl + 2NaCN \leftrightharpoons Na [Ag(CN)2] + NaCl.

The reaction with the sulphide is reversible and accumulation of Na­2S must be prevented. A free excess of air is continuously passed through the solution which oxidizes Na2S into sulphate and thiosulphate.

2Na2 + 2O2 + H2O → Na2S2O3 + 2NaOH

Na2S2O3 + 2NaOH + 2O2 → 2Na2SO4 + H2O

2Na[Ag(CN)2] + 4NaOH + Zn → Na2ZnO2 +4NaCN + 2H2O + 2Ag

Compounds of silver : AgNO3, Ag2S, AgCl, AgBr, AgI, and AgO

 

d Block Elements : Murcury and its Compounds