Mercuric Chloride or Corrosive Sublimate (HgCl20)

    Preparation:-

    It is obtained by dissolving mercurice oxide in HCl

    HgO + 2HCl           →                HgCl2 + H2O

     

    Commercially, it is obtained by heating Hgso4 with NaCl in presence of MnO2



    HgSO4 + NaCl                    →                Na2SO4 + HgCl2

    MnO2 is added to prevent the reduction of mercuric chloride to mercurous chloride.

     

    Properties:-

     

    1. It is white needle – shaped crystalline solid soluble in water.

     

    1. Action of Heat:-

    On heating, it decomposes forming mercury and chlorine.

    HgCl2                   →                   Hg + Cl2

     

    1. Action of KI:-

    When KI is added to Hgcl2 solution, give red ppt of mercuric iodided which on adding excess KI dissolve forming a complete potassium tetra iodo mercurate

     

    HgCl2 + KI               →              HgI2 + 2KCl

    HgI2 + KI                →                K2 (HgI4)

    Excess                                 potassium tetra iodo mercurate.

    Alkaline solution of K2 (HgI4) is called Nesseler’s reagent which is used for detection of Ammonia and its compounds.

     

    1. Action of NH3:-

    Ammonia gives a white ppt of mercuric amino chloride with HgCl2.

    HgCl2+2NH3               →             Hg(NH2)Cl + NH4Cl

    Mercuric amino chloride

    White ppt

    1. Action of SnCl2:-

    SnCl2 reduce mercuric chloride to mercurous chloride which appears as white ppt and on further reduction it gives black ppt of mercury.

    HgCl2 + SnCl2             →            Hg2Cl2 +SnCl4

    Mercurous chloride (white ppt)

    Hg2Cl2 +SnCl2           →             Hg + SnCl4

    Excess                         Black ppt

    1. Action of SO2:-

    SO2 reduce HgCl2 in solution to give white ppt of mercurous chloride.

    2HgCl2 + So4 + H2O                 →          Hg2Cl2 + H2SO4 + 2HCl

    White ppt

    1. Action of NaOH:-

    With HgCl2 solution, NaOH gives a yellow ppt of mercurous oxide.

    HgCl2 + 2NaOH                 →                HgO +2NaCl +H2O

     

    Uses:-

    • it is used in making Nesseler’s reagent.
    • It is used as on anticept for sterization of surgical instruments.

     

    • It is used as preservative for timber.