CHEMCA Free Chemistry Notes for JEE NEET Chemistry MadeEasy: Salt Analysis: Anions (Acid Radicals)

Anions are classified into three groups based on their reaction with acids.

1. Group I (Dilute $H_2SO_4$ Group)

These anions liberate gases with Dilute $H_2SO_4$.

A. Carbonate ($CO_3^{2-}$): Brisk effervescence of $CO_2$ (turns lime water milky).

B. Sulphide ($S^{2-}$): Smell of rotten eggs ($H_2S$). Turns Lead Acetate paper black.

C. Sulphite ($SO_3^{2-}$): Smell of burning sulphur ($SO_2$). Turns acidified $K_2Cr_2O_7$ paper green.

D. Nitrite ($NO_2^{-}$): Reddish-brown fumes of $NO_2$.

These anions react with Conc. $H_2SO_4$ but not dilute acid.

A. Chloride ($Cl^-$): Pungent fumes of $HCl$. White dense fumes with $NH_4OH$.

Chromyl Chloride Test: Salt + $K_2Cr_2O_7$ + Conc. $H_2SO_4 \rightarrow$ Red Vapours ($CrO_2Cl_2$).

B. Bromide ($Br^-$): Reddish-brown fumes of $Br_2$. Turns starch paper yellow.

C. Iodide ($I^-$): Violet fumes of $I_2$. Turns starch paper blue.

D. Nitrate ($NO_3^-$): Brown fumes of $NO_2$ intensified by adding Copper turnings.

Brown Ring Test: Salt Soln + Fresh $FeSO_4$ + Conc. $H_2SO_4$ (along sides) $\rightarrow$ Brown Ring $[Fe(H_2O)_5NO]^{2+}$.

E. Acetate ($CH_3COO^-$): Smell of Vinegar.

Identified by specific wet tests (do not react with acids to evolve gas).

A. Sulphate ($SO_4^{2-}$): White ppt with $BaCl_2$, insoluble in conc. $HCl$.

$$ SO_4^{2-} + BaCl_2 \rightarrow BaSO_4 \downarrow \text{ (White)} + 2Cl^- $$

B. Phosphate ($PO_4^{3-}$): Canary yellow ppt with Ammonium Molybdate + Conc. $HNO_3$.