Test for Mercury(II) ion

Test for Mercury(II) ion

1.      Hydrogen Sulphide test:

In the presence of dilute HCl, initially a white ppt is formed. When further amount of hydrogen sulphide is added, a black ppt is formed.

3Hg2+ + 2Cl + 2H2S → Hg3S2Cl2↓ + 4H+

Hg3S2Cl2↓ + H2S → 3HgS↓ + 2H+ + 2Cl

2.      Ammonia test:

When treated with ammonium hydroxide solution, a white ppt is formed.

2Hg2+ + NO3 + 4NH3 + H2O → HgO.Hg(NH2)NO3↓ + 3NH4+

3.      Sodium hydroxide test:

When small amount of sodium hydroxide is added, a yellow ppt is obtained.(If exact stoichiometric amount is not used, brownish-red ppt is obtained)

Hg2+ + 2OH →HgO↓ + H2O

4.      Potassium iodide test:

When potassium iodide is slowly added a red ppt is obtained. The ppt dissolves in excess to form tetraiodomercurate(II) ion.

Hg2+ + 2I → HgI2

HgI2 + 2I → [HgI4]2-

5.      Tin(II) chloride test:

When moderate amount of tin(II) chloride is added, a white silky ppt is formed.

2Hg2+ + Sn2+ + 2Cl → Hg2Cl2↓ + Sn4+

If excess reagent is added, black ppt of mercury is forme

Hg2Cl2 + Sn2+ → 2Hg↓ + Sn4+ + 2Cl

6.      Diencuprato(II) sulphate test:

When the sample solution is treated with di(ethylenediamine)cuprato(II) sulphate reagent in present of KI, a dark blue-violet ppt is formed.

Hg2+ + 4I → [HgI4]2-

[Cu(en)2]2+ + [HgI4]2- → [Cu(en)2][HgI4]↓

7.      Cobalt(II) thiocyanate test:

To the sample solution Cobalt(II) thiocyanate solution is added, when a deep-blue crystalline ppt is obtained.

Hg2+ + Co2+ + 4SCN → Co[Hg(SCN)4]↓

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