Common anions — Cl⁻, Br⁻, I⁻, SO₄²⁻, NO₃⁻, CO₃²⁻ — confirmatory tests

3.5.2 · Chemistry › Inorganic Qualitative Analysis

1. Halides: Cl⁻, Br⁻, I⁻

YE KAISE kaam karta hai (logic ki derivation): Ag⁺ ek soft-ish cation hai jo halides se strongly bind karta hai. Jaise hum Cl⁻ → Br⁻ → I⁻ jaate hain, anion bada aur zyada polarisable (softer) hota jaata hai, to bond zyada covalent hoti jaati hai, salt kam soluble hota jaata hai, aur NH₃ mein bhi kam soluble hota hai (kyunki NH₃ sirf zyada ionic, higher-Ksp salts ko re-dissolve kar sakta hai).

${\text{Ag}}^{+}+{\text{X}}^{-}\to \text{AgX}\downarrow$ $\text{AgCl}+2{\text{NH}}_3\to [{\text{Ag(NH}}_3{)}_2{]}^{+}+{\text{Cl}}^{-}$

1b. Br⁻ aur I⁻ ko oxidation se confirm karna (the "layer test")

Halide oxidation ki aasaani: ${\text{I}}^{-}>{\text{Br}}^{-}>{\text{Cl}}^{-}$ (bada ion → electron zyada aasaani se chhodata hai). Chlorine water dalo (ya Cl₂/conc. H₂SO₄ + MnO₂), phir CCl₄/CHCl₃ se shake karo:

${\text{Cl}}_2+2{\text{Br}}^{-}\to 2{\text{Cl}}^{-}+{\text{Br}}_2(\text{orange organic layer})$ ${\text{Cl}}_2+2{\text{I}}^{-}\to 2{\text{Cl}}^{-}+{\text{I}}_2(\text{violet/purple organic layer})$

• Cl₂ Cl⁻ ko oxidise nahi kar sakta → koi test nahi, isse ye distinguish hota hai.
• I⁻ se starch blue-black bhi ho jaata hai (classic confirmation).

2. Sulphate, SO₄²⁻

${\text{Ba}}^{2+}+{\text{SO}}_4^{2-}\to {\text{BaSO}}_4\downarrow (\text{white})$

3. Nitrate, NO₃⁻

HOW (chemistry): conc. H₂SO₄ oxidising conditions generate karta hai; nitrate reduce hokar NO banta hai, jo Fe²⁺ ke saath complex bana leta hai:

$3{\text{Fe}}^{2+}+4{\text{H}}^{+}+{\text{NO}}_3^{-}\to 3{\text{Fe}}^{3+}+\text{NO}+2{\text{H}}_2\text{O}$ $\text{NO}+[{\text{Fe(H}}_2{\text{O)}}_6{]}^{2+}\to [{\text{Fe(H}}_2{\text{O)}}_5\text{NO}{]}^{2+}+{\text{H}}_2\text{O}$

Complex $[{\text{Fe(H}}_2{\text{O)}}_5\text{NO}{]}^{2+}$ brown color ka hota hai. Ring kyun banti hai? Acid dense hai aur sink karta hai; reaction sirf boundary layer par hoti hai jahan concentrations milte hain → brown wahan banta hai.

4. Carbonate, CO₃²⁻

${\text{CO}}_3^{2-}+2{\text{H}}^{+}\to {\text{H}}_2\text{O}+{\text{CO}}_2\uparrow$ ${\text{CO}}_2+{\text{Ca(OH)}}_2\to {\text{CaCO}}_3\downarrow +{\text{H}}_2\text{O}(\text{milky})$

Common Mistakes (Steel-man + fix)

Active-Recall Flashcards

#flashcards/chemistry

Connections

• Group Analysis of Cations — same precipitation logic, opposite ion
• Solubility Product (Ksp) — AgX selectivity ka quantitative basis
• Redox Series and Standard Potentials — I⁻ sabse aasaan kyun oxidise hota hai
• Coordination Complexes — [Ag(NH₃)₂]⁺ aur [Fe(H₂O)₅NO]²⁺
• Acid–Base Reactions of Salts — carbonate effervescence
• Polarisation and Fajans' Rules — Cl→I mein covalent character se color/insolubility explain hoti hai

Concept Map