Mercurous Chloride or Calomel (Hg2Cl2)



Preparation:-

 

1. It is obtain by adding HCl to mercurous Nitrate solution.

Hg2 (NO3)2 +2HCl          →         Hg2Cl2 +2HNO3

white

2. It is obtained by heating mercuric chloride with Hg.

HgCl2+Hg      →             Hg2Cl2

 

3. Commercially it is obtained by heating HgSO4 and NaCl with Hg.

HgSO4 + Hg + NaCl                 →           Hg2Cl2 + Na2SO4

 

Properties:-

 

1. It is white amorphous solid insoluble in water.

2. When heated strongly, it decomposes forming HgCl2 and Hg.

Hg2Cl2                          →           HgCl2 +Hg

 

3. Dissolves in aqueregia, forming mercuric chloride.

3HCl + HNO3                    →                             NOCl + 2H2O +2Cl

Hg2Cl2 + 2Cl                          →                2HgCl2

Hg2Cl2 + 3Hcl +HNO3        →                2HgCl2 + NoCl + 2H2O

 

4. Action of NH3:-

With NH3, Hg2 gives a black ppt of mercury and mercuric amino chloride,

Hg2Cl2 + NH3            →             Hg + Hg (NH2) Cl + NH4Cl

 

Uses:-

  • It is used medicine as mild purgative.
  • It is used in making calomel electrode.