Chemistry XII Content
Mercuric Chloride or Corrosive Sublimate (HgCl20)
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.
- 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
- 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
- Action of NaOH:-
With HgCl2 solution, NaOH gives a yellow ppt of mercurous oxide.
HgCl2 + 2NaOH → HgO +2NaCl +H2O
- 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.