Silver ( Chemistry Notes )

 SILVER(Ag)

  

Chief ore of silver

1.       Argentite ( Ag₂S )

2.      Horn Silver ( AgCl )

 

EXTRACTION OF SILVER FROM CYANIDE PROCESS

1.     Crushing and Pulverizing
Big lumps of ore are crushed into small pieces with the help of a jaw crusher, which is further pulverized with the help of a pulverizer.

2.    Concentration
The powdered is concentrated by the froth floatation process. In this process, powder ore is mixed with water and little amount of pine oil. Then, this mixer is kept in a rectangular tank. The mixer in a tank is agitated by passing compressed air. Due to agitation, impurities being hydrophilic in nature gets preferentially wetted by water and settle down in the bottom of the tank whereas sulphide ore being hydrophobic in nature gets preferentially wetted by pine oil and floats on the surface as froth which can be skimmed off.

 

3.    Treatment with NaCN solution
The concentrated ore is treated with sodium cyanide solution to obtain the mixture of sodium argentocyanide and sodium sulphide. Thus, obtained mixture is then agitated by passing air to remove sodium sulphide in the form of sodium sulphate.
Ag₂ + 4 NaCN   --------> 2 Na [ Ag (CN)₂] + Na₂S
           Na₂S       ---------> Na₂SO₄

4.    Recovery of Metal
Thus, Obtained sodium Argentocyanide is then treated with electro-positive metal i.e. Zinc, to obtain the precipitate of silver metal. Thus, obtained silvered is then filtered and dried out, which is called spongy silver.
 2 Na [ Ag (CN)₂] + Zn --------. Na₂ [ Zn (CN)₄] + 2 Ag

           5.       Refining
Thus, Obtained silver contains the impurities such as As, Sb, Zn, etc. which has to be purified. Purification can be done by the electrolytic process. In this process, the pure sheet of silver metal is made the cathode and impure silver is made anode. Acidified silver nitrate solution is used as an electrolyte. On passing electricity pure silver get deposited at the cathode and the impurity is left below anode as anode mud.
     At anode,         Ag          ----- Ag⁺ + e^-
   At cathode,    Ag⁺ + e^-  ------   Ag

 

Uses of silver

1.       Used to make ornament items

2.       Used to make coin

3.       Used to make teeth

 

 

Compounds of silver

1.       Silver nitrate ( AgNO₃ )
It can be prepared by dissolving silver in nitric acid solution and evaporating the resulting solution up to the crystallization point to get the crystal.
     Ag + HNO_{3  ---------------}AgNO₃ + NO₂ + H₂O

     AgNO₃(aq) ------_evaporating------ AgNO₃ (crystal)

 

Uses
- used as lab reagents
- used to prepare photographic paper
- used as indelible ink

 

2.       Silver chloride
It can be prepared by the action of AgNO₃ with chloride salt.
AgNO₃   + NaCl ------ AgCl  + NaNO₃

AgNO₃   + KCl   ------ AgCl  + KNO₃

Uses
- used as photographic film
- used as photographic paper
- used as a reference electrode

 

 

* While silver nitrate solution leaves a permanent black stain on the skin on exposure to sunlight?
= when silver nitrate solution comes in contact with our skin in presence of sunlight, the organic matter present in the skin reduces AgNO₃ into the free silver metal which leaves a permanent black stain due to it leaves a permanent black stain on the skin on exposure to sunlight.

2AgNO₃   + organic matter  ---- _sunlight --- -à2Ag  + NO₂  + O₂