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.

 

2. Action of Heat:-

On heating, it decomposes forming mercury and chlorine.

            HgCl2                   →                   Hg + Cl2

 

3. 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.

 

4. 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

5. 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

6. Action of SO2:-

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

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

                                                                        White ppt

7. 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.


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