Mercurous Chloride Or Calomel (Hg2Cl2)

Preparation:

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

• It is obtained by heating mercuric chloride with Hg.
  HgCl2+Hg → Hg2Cl2

• Commercially it is obtained by heating HgSO4 and NaCl with Hg.
  HgSO4 + Hg + NaCl → Hg2Cl2 + Na2SO4

Properties:

• It is white amorphous solid insoluble in water.

• When heated strongly, it decomposes forming HgCl2 and Hg.
  Hg2Cl2 → HgCl2 +Hg

• Dissolves in aqueregia, forming mercuric chloride.
  3HCl + HNO3 → NOCl + 2H2O +2Cl
  Hg2Cl2 + 2Cl → 2HgCl2
  Hg2Cl2 + 3Hcl +HNO3 → 2HgCl2 + NoCl + 2H2O

• 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.