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:

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

• Action of heat:

On heating, it decomposes forming mercury and chlorine.

HgCl2 → Hg + Cl2

• 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.

• 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

• 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

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

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

*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.