Mercurous Chloride or Calomel (Hg2Cl2)


1. It is obtain by adding HCl to mercurous Nitrate solution.
Hg2 (NO3)2 +2HCl          →         Hg2Cl2 +2HNO3
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


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


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