Important Qualitative Analysis Formulas for JEE and NEET

Charcoal Cavity Test:

Cobalt Nitrate Test:

Flame test :

Borax Bead test:

Analysis of ANIONS (Acidic Radicals) :
(a) DILUTE SULPHURIC ACID/DILUTE HYDROCHLORIC ACID GROUP :
1. CARBONATE ION (CO₃^2-_​) :

• Dilute H₂SO₄ test : A colourless odourless gas is evolved with brisk effervescence.
  CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂↑
• Lime water/Baryta water (Ba(OH)₂) test:
  CO₂ + Ca(OH)₂ → CaCO₃↓, (milky) + H₂O
  

2. SULPHITE ION ( SO₃^2-) :

• Dilute H₂SO₄ test :
  CaSO₃ + H₂SO₄ → CaSO₄ + H₂O + SO₂↑ ; SO₂ has suffocating odour of burning sulphur.
• Acidified potassium dichromate test : The filter paper dipped in acidified K₂Cr₂O₇ turns green.
  
• Barium chloride/Strontium chloride solution :

White precipitate dissolves in dilute HCI. BaSO₃ ↓ + 2H⁺ → Ba²⁺ + SO₂ ↑ + H₂O.

3. SULPHIDE ION (S^2-):

• Dilute H₂SO₄ test : Pungent smelling gas like that of rotten egg is obtained.
  S^2- + 2H⁺ → H₂S↑
• Lead acetate test : (CH₃COO)₂Pb + H₂S → PbS↓ (black) + 2CH₃COOH. 
• Sodium nitroprusside test: Purple coloration is obtained.
  S^2- + [Fe(CN)₅ (NO)]^2- → [Fe(CN)₅NOS]^4- (violet).
• Cadmium carbonate suspension/ Cadmium acetate solution :
  Na₂S + CdCO₃ → CdS↓ (Yellow) + Na₂CO₃

4. NITRITE ION ( NO^​₂^-):

• Dilute H₂SO₄ test :
  NO₂^- + H⁺ → HNO₂ ; (2 HNO₂ → H₂O + N₂O₃);
  3HNO₂ → HNO₃ + 2NO + H₂O ; 2NO + O₂ → 2NO₂ ↑
• Starch iodide test:
  

5. ACETATE ION (CH₃COO^-)

• Dilute H₂SO₄ test : (CH₃COO)₂Ca + H₂SO₄ → 2CH₃COOH (vinegar like smell) + CaSO₄
• Neutral ferric chloride test :
  
  

(b) CONC. H₂SO₄ GROUP :
1. CHLORIDE ION (Cl^-):

• Concentrated H2SO4 test : Cl^- + H₂SO₄ → HCI (colourless pungent smelling gas) + HSO₄^-
• NH₄OH + HCI → NH₄CI ↑ (white fumes) + H₂O.
• Silver nitrate test : Cl^- + Ag⁺ → AgCI↓ (white)

White precipitate is soluble in aqueous ammonia and precipitate reappears with HNO₃.
AgCI + 2NH₄OH → [ Ag(NH₃)₂]CI (Soluble) + 2H₂O ; [Ag(NH₃)₂]CI + 2H⁺ → AgCI↓ + 2NH₄⁺.

• Chromyl chloride test:
  2. BROMIDE ION (Br^-) :
• Concentrated H₂SO₄ test :
  2NaBr + H₂SO₄ → Na₂SO₄ + 2HBr ; 2HBr + H₂SO₄→ Br₂ ↑ (reddish-brown) + 2H₂O + SO₂
• Silver nitrate test : NaBr + AgNO₃ → AgBr↓ (pale yellow) + NaNO₃

Yellow precipitate is partially soluble in dilute aqueous ammonia but readily dissolves in concentrated ammonia solution. AgBr + 2NH₄OH → [Ag(NH₃)₂] Br + H₂O

• Chlorine water test (organic layer test):
  2Br^- + Cl₂ → 2CI^- + Br₂ ↑.
  Br₂ + CHCI₃ / CCI₄ → Br₂ dissolve to give reddish brown colour in organic layer.
  3. IODIDE ION (I^-) :
• Concentrated H₂SO₄ test : 2Nal + H₂SO₄ → Na₂SO₄ + 2HI
  2HI + H₂SO₄ → l₂ ↑ (pungent smelling dark violet) + 2H₂O + SO₂
• Starch paper test: Iodides are readily oxidised in acid solution to free iodine; the free iodine may than be identified by deep blue colouration produced with starch solution.
  3I^- + 2NO₂^- + 4H⁺ → l₃^- + 2NO ↑ + 2H₂O.
• Silver nitrate test : Bright yellow precipitate is formed.
  I^- + Ag⁺ → Agl↓

Bright yellow precipitate is insoluble in dilute aqueous ammonia but is partially soluble in concentrated ammonia solution.

• Chlorine water test (organic layer test):
  2Nal + Cl₂ → 2NaCI + l₂
  l₂ + CHCI₃ → l₂ dissolves to give violet colour in organic layer.
  4. NITRATE ION (NO₃^-) :
• Concentrated H₂SO₄ test: Pungent smelling reddish brown vapours are evolved.
  

Addition of bright copper turnings or paper pellets intensifies the evolution of reddish brown gas.

• Brown ring test:
  

3. Miscellaneous Group :
1. SULPHATE ION (SO₄^2-) :

• Barium chloride test : Na₂SO₄ + BaCI₂ → BaSO₄↓ (white) + 2NaCI.

White precipitate is insoluble in warm dil. HNO₃ as well as HCI but moderately soluble in boiling concentrated hydrochloric acid.

• Lead acetate test : Na₂SO₄ + (CH₃COO)₂Pb → PbSO₄ ↓ (White) + 2CH₃COONa

White precipitate soluble in excess of hot ammonium acetate.
PbSO₄ + 2CH₃COONH₄ → (CH₃COO)₂Pb (soluble) + (NH₄)₂SO₄
2. PHOSPHATE ION (PO₄^3-):

• Ammonium molybdate test:
  Na₂ HPO₄ (aq) + 12(NH₄)₂MoO₄ + 23HNO₃ → (NH₄)₃PMo₁₂O₄₀↓ (canary yellow) + 2NaNO₃ + 21NH₄NO₃ + 12H₂O

ANALYSIS OF CATIONS
1. AMMONIUM ION (NH₄⁺) :
2NH₃ + Mn²⁺ + H₂O₂ + H₂O → MnO(OH)₂ ↓ (brown) + 2NH₄⁺

Nessler's reagent (Alkaline solution of potassium tetraidomercurate(ll):

I^st GROUP (Pb²⁺, Hg₂²⁺, Ag⁺):

IIA Group (Hg²⁺, Pb²⁺, Bi³⁺, Cu²⁺, Cd²⁺)

IIB Group (As³⁺, Sb³⁺, Sn²⁺, Sn⁴⁺)

III^rd Group (Al⁺³, Cr⁺³, Fe⁺³)

IV^th GROUP (Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺)

V^th Group (Ba²⁺, Sr²⁺, Ca²⁺) :

VI^th GROUP :
MAGNESIUM ION (Mg²⁺) :

Titan Yelllow (a water soluble yellow dyestuff): It is adsorbed by Mg(OH)₂ producing a deep red colour or precipitate.