Test for Mercury(I) ion


 Dilute HCl test:

When dilute HCl or any soluble chloride is added, a white ppt of mercury(I) chloride is obtained.

Hg22+ + 2Cl →Hg2Cl2 ↓

The ppt is insoluble in dilute acids.

2.     Hydrogen sulphide test:

When H2S gas is passed, a black ppt is obtained.

Hg22+ + H2S →Hg ↓ + HgS↓ + 2H+

3.     Ammonia test:

When treated with ammonia solution, a black ppt if formed.

2Hg22++ NO3+4NH3+H2O → HgO.Hg(NH2)(NO3) ↓(Basic mercury(I) amidonitrate)+2Hg↓+3NH4+


4.     Sodium hydroxide test:

When sodium hydroxide is added, a black ppt is formed. The ppt is insoluble in excess NaOH , but dissolves in dilute nitric acid.

Hg22+ + 2OH → Hg2O↓ + H2O

When boiled, the black colour turns to grey .

Hg2O →HgO↓ + Hg↓

5.     Potassium chromate test:

When treated with hot potassium chromate solution, a red crystalline ppt of mercury(I) chromate is formed. ( when cold potassium chromate solution is used, a brown ppt is formed). The red ppt turns black on treatment with NaOH solution.

Hg22+ + CrO42- → Hg2CrO4

Hg2CrO+ 2OH →Hg2O ↓ + CrO42- + H2O

6.     Potassium Iodide test:

When potassium iodide is slowly added to cold mercury(I) solution, a green ppt is obtained.

Hg22+ + 2I →Hg2I2

When excess reagent is used, black mercury deposit out.

Hg2I2 + 2I →[HgI4]2- + Hg↓

7.     Sodium carbonate test:

When sodium carbonate solution is added to the cold mercury(I) solution, yellow ppt is obtained.

Hg22+ + CO32- → Hg2CO3

The yellow ppt slowly turns to blackish grey.

Hg2CO→HgO ↓ + Hg↓ + CO2

8.     Disodium hydrogen phosphate test:

When Disodium hydrogen phosphate solution is added, a white ppt is obtained.

Hg22+ + HPO42- → Hg2HPO4

9.     Copper coin test:

If a drop of mercury(I) nitrate solution is added on a glossy copper coin, a glittery , silverish spot is formed.

Cu + Hg22+ → Cu2+ + 2Hg ↓

10.            Diphenylcarbazide test:


When diphenylcarbazide solution is added, a violet-coloured compound is formed.

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