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↓
Hg2CrO4 + 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.
Hg2CO3 →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.