Chemistry of Corrosive Sublimate

General method of preparation:

1. When excess amount of chlorine is passed over mercury, mercuric chloride is formed.
$$\ce{Hg + Cl2 ->HgCl2}$$

2. When mercury is heated with conc. H2SO4, mercuric sulphate is formed which is further heated with NaCl in presence of MnO2, sublimate of mercuric chloride is formed.
$$\ce{Hg + conc. H2SO4->[\Delta]HgSO4 + H2O + SO2}$$
$$\ce{HgSO4 + 2NaCl + Hg->[\Delta][\ce{MnO2}]HgCl2 + Na2SO4}$$

Note: MNO2 prevents the formation of mercurous chloride i.e. calomel.

3. When mercury is treated with aqua regia, corrosive sublimate is formed.
$$\ce{Hg + 3HCl + HNO3->HgCl2 + NO2Cl + H2O}$$

Physical properties:

  •  It is sparangly soluble in cold water but soluble in hot water.
  •  It’s melting point is 276oC and boiling point is 303oC.
  • It is highly poisonous compound.

Chemical Properties:

1. Action with Stannous chloride: When mercuric chloride is treated with less amount of stannous chloride, at first white ppt of mercuric chloride is formed but when it is treated with excess amount of stannous chloride, it gets reduced to mercury.
$$\ce{HgCl2 + $\underset{\text{Less}}{\ce{SnCl2}}$->Hg2Cl2 + SnCl4}$$
$$\ce{Hg2Cl2 + $\underset{\text{Excss}}{\ce{SnCl2}}$ ->Hg + SnCl4}$$

2. Action with potassium iodide solution: When mercuric iodide is treated with less amount of KI solution, brown precipitation of mercuric iodide is formed. But, when it is treated with excess KI solution, di-potassium mercuric iodide is formed.
$$\ce{HgCl2 + 2KI->HgI2 v + 2KCl}$$
$$\ce{HgCl2 + 2KI->$\underset{\text{Di-potassium mercuric iodide}}{\ce{K2[HgI4]}}$}$$

3. Reaction with Ammonia: Ammonia forms an infusible white ppt. of mercuric amino chloride.

$$\ce{HgCl2 + 2NH3->$\underset{\text{Mercuric Aminochloride}}{\ce{HgNH2Cl}}$ + NH4Cl}$$

4. Action with H2S: In its acidic solution gives black ppt of HgS.
$$\ce{HgCl2 + H2S->HgS + 2HCl}$$

Uses:

  • It is used as an antiseptic and germicides.
  • It is used for washing the surgical instruments before the operation.
  • It is used in the preservation of wood and fur.
  • It is used in dry cell.

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