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Chemistry 12 Notes for Chemistry Notes

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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.

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