Qualitative Analysis of Iodide Ion
On adding concentrated H2SO4 to a salt, if violet fumes with pungent smell evolved and black specks appeared on the sides of the test tube, I– is present.
MI + H2SO4 → MHSO4 + HI
HI + 2H2SO4 → 2H2O + SO2 + I2
Confirmatory Test
Silver Nitrate Test
A yellow precipitate is obtained on adding AgNO3 solution to acidified (with dil HNO3) water solution, which is insoluble in NH4OH.
Ag+ + I– → Agl ↓ (Silver iodide, yellow precipitate)
Organic Layer Test
The addition of chlorine water to test solution liberates free iodine, which colours the solution, violet. On shaking with carbon tetra chloride, a violet colour is imparted to the organic layer.
2NaI + Cl2 → 2NaCl + I2 (Iodine, Violet Colour in CCl4)