Inorganic ChemistryHigh Yield (2 Qs in JEE Main)

Principles of Practical Chemistry & Salt Analysis Formulas

Systematic qualitative analysis of cations (Groups 0 to VI) and anions, confirmatory tests, flame tests, borax bead test, and organic functional group identification.

8 Formulas•512+ Questions in Bank

Core Formulas & Mathematical Identities

Cation Group Separation Scheme (Groups 0 to VI)

\begin{array}{llll} \text{Group} & \text{Reagent} & \text{Cations} & \text{Precipitate Form} \\ \text{0} & \text{NaOH} & \text{NH}_4^+ & \text{NH}_3\uparrow \text{ (Nessler's reagent: brown ppt)} \\ \text{I} & \text{Dil. HCl} & \text{Pb}^{2+}, \text{Ag}^+, \text{Hg}_2^{2+} & \text{Chlorides (PbCl}_2 \text{ white, hot-water sol.)} \\ \text{II-A/B} & \text{H}_2\text{S + dil. HCl} & \text{Cu}^{2+}, \text{Pb}^{2+}, \text{Bi}^{3+}, \text{Cd}^{2+}, \text{As}^{3+} & \text{Sulphides (CuS black, CdS yellow, As}_2\text{S}_3 \text{ yellow)} \\ \text{III} & \text{NH}_4\text{OH + NH}_4\text{Cl} & \text{Fe}^{3+}, \text{Al}^{3+}, \text{Cr}^{3+} & \text{Hydroxides (Fe(OH)}_3 \text{ brown, Al(OH)}_3 \text{ gelatinous, Cr(OH)}_3 \text{ green)} \\ \text{IV} & \text{H}_2\text{S + NH}_4\text{OH} & \text{Co}^{2+}, \text{Ni}^{2+}, \text{Zn}^{2+}, \text{Mn}^{2+} & \text{Sulphides (ZnS dirty white, MnS buff/flesh, CoS/NiS black)} \\ \text{V} & (\text{NH}_4)_2\text{CO}_3 & \text{Ba}^{2+}, \text{Sr}^{2+}, \text{Ca}^{2+} & \text{Carbonates (white)} \\ \text{VI} & \text{Na}_2\text{HPO}_4 & \text{Mg}^{2+} & \text{Mg(NH}_4)\text{PO}_4 \text{ (white crystalline)} \end{array}

Systematic precipitation order governed by solubility product (K_sp). Group II sulphides have very low K_sp and precipitate even with low S²⁻ in acid; Group IV sulphides have higher K_sp and require basic medium.

Examiner Tip: NH₄Cl is added before NH₄OH in Group III to suppress OH⁻ concentration by common ion effect, preventing premature precipitation of Group IV and Mg(OH)₂.

Confirmatory Tests for Acid Radicals (Anions)

\text{Brown Ring: } \text{Fe}^{2+} + \text{NO}_3^- + \text{H}_2\text{SO}_4 \to [\text{Fe}(\text{H}_2\text{O})_5(\text{NO})]^{2+} \; (\text{Brown ring at interface, Fe in +1 OS})

Key confirmatory tests for anions: Nitrate (Brown Ring test), Chloride (Chromyl Chloride test), Sulphate (BaCl₂ gives white BaSO₄ insoluble in conc. HCl), and Carbonate (CO₂ turns lime water milky).

Examiner Tip: In [Fe(H₂O)₅(NO)]²⁺, NO exists as NO⁺ (nitrosonium), so oxidation state of Fe is +1 (paramagnetic, 3 unpaired electrons, μ = 3.87 BM).

Chromyl Chloride Test (Chloride Detection)

4\text{NaCl} + \text{K}_2\text{Cr}_2\text{O}_7 + 6\text{H}_2\text{SO}_4 \xrightarrow{\Delta} 2\text{CrO}_2\text{Cl}_2\uparrow \text{ (Deep red-brown vapor)} \xrightarrow{+\text{NaOH}} \text{Na}_2\text{CrO}_4 \text{ (Yellow)} \xrightarrow{+\text{Pb(OAc)}_2} \text{PbCrO}_4\downarrow \text{ (Yellow ppt)}

Confirmatory test for ionic chlorides. Heating solid chloride with potassium dichromate and conc. H₂SO₄ liberates red-brown vapors of chromyl chloride (CrO₂Cl₂).

Examiner Tip: Bromides and iodides evolve Br₂ (reddish) and I₂ (violet), but their vapors do NOT give a yellow precipitate with lead acetate. Does not work for AgCl, PbCl₂, Hg₂Cl₂.

Flame Test Characteristic Colors

\begin{array}{llll} \text{Metal} & \text{Color} & \text{Metal} & \text{Color} \\ \text{Li} & \text{Crimson red} & \text{Ca} & \text{Brick red} \\ \text{Na} & \text{Golden yellow} & \text{Sr} & \text{Crimson red} \\ \text{K} & \text{Violet / Lilac} & \text{Ba} & \text{Apple green} \\ \text{Rb} & \text{Red-violet} & \text{Cu} & \text{Blue-green} \\ \text{Cs} & \text{Blue} & \text{Pb} & \text{Greyish-white} \end{array}

Excitation of valence electrons by Bunsen flame imparts characteristic emission spectrum colours. Beryllium (Be) and Magnesium (Mg) do NOT give flame colour due to high ionization enthalpy.

Examiner Tip: Viewing through cobalt blue glass: Sodium yellow is absorbed (invisible); Potassium lilac appears crimson/violet.

Borax Bead Test (Metaborate Formation)

\text{Na}_2\text{B}_4\text{O}_7\cdot 10\text{H}_2\text{O} \xrightarrow{\Delta} \text{Na}_2\text{B}_4\text{O}_7 \xrightarrow{\text{strong }\Delta} 2\text{NaBO}_2 + \text{B}_2\text{O}_3 \; (\text{Glassy bead}) \xrightarrow{+\text{CoO}} \text{Co(BO}_2)_2 \; (\text{Deep Blue})

Heating borax with transition metal salts forms characteristic colored metaborate beads in oxidizing and reducing flames.

Examiner Tip: Key bead colors in oxidizing flame: Cobalt (Deep Blue), Copper (Blue in hot/cold), Chromium (Green), Iron (Yellow in cold, brown in hot), Manganese (Violet/Amethyst).

Organic Functional Group Detection Tests

\begin{array}{lll} \text{Functional Group} & \text{Test Reagent} & \text{Observation} \\ \text{Unsaturation (C=C)} & \text{Br}_2/\text{CCl}_4 \;\text{or}\; \text{Bayer's (alk. KMnO}_4) & \text{Decolourization} \\ \text{Alcoholic (-OH)} & \text{Ceric Ammonium Nitrate (CAN)} & \text{Red coloration} \\ \text{Phenolic (-OH)} & \text{Neutral FeCl}_3 & \text{Violet/purple coloration} \\ \text{Carbonyl (C=O)} & \text{2,4-DNP (Brady's reagent)} & \text{Orange-yellow precipitate} \\ \text{Aldehyde (-CHO)} & \text{Tollens' reagent } [\text{Ag(NH}_3)_2]^+ & \text{Silver mirror on tube wall} \\ \text{Aldehyde (aliphatic)} & \text{Fehling's solution (A+B)} & \text{Red precipitate (Cu}_2\text{O)} \\ \text{Carboxylic (-COOH)} & \text{Sat. NaHCO}_3 & \text{Brisk effervescence of CO}_2\uparrow \\ \text{1° Amine (-NH}_2) & \text{CHCl}_3 + \text{alc. KOH (Carbylamine)} & \text{Foul smelling isocyanide (R-NC)} \end{array}

Standard organic functional group identification tests prescribed in the JEE practical chemistry curriculum.

Examiner Tip: Lucas test for alcohol classification: ZnCl₂ + conc. HCl: 3° alcohol gives immediate turbidity; 2° takes 5 mins; 1° does not react at room temperature.

Nessler's Reagent & Ammonium Detection

\text{Nessler's Reagent: } \text{K}_2[\text{HgI}_4] \; (\text{alkaline solution}), \quad 2[\text{HgI}_4]^{2-} + \text{NH}_4^+ + 4\text{OH}^- \to \text{HgO}\cdot\text{Hg}(\text{NH}_2)\text{I}\downarrow \text{ (Brown ppt: Iodide of Millon's base)} + 7\text{I}^- + 3\text{H}_2\text{O}

Potassium tetraiodomercurate(II) in alkaline KOH precipitates brown iodide of Millon's base with trace quantities of ammonium ions or ammonia.

Examiner Tip: Very sensitive test: even tap water traces of ammonia produce distinct yellow-brown coloration.

Mohr's Salt & Potash Alum Preparation

\text{Mohr's Salt: } \text{FeSO}_4\cdot(\text{NH}_4)_2\text{SO}_4\cdot 6\text{H}_2\text{O}, \quad \text{Potash Alum: } \text{K}_2\text{SO}_4\cdot\text{Al}_2(\text{SO}_4)_3\cdot 24\text{H}_2\text{O}

Standard double salts synthesized by equimolar crystallization in acidic medium to prevent hydrolysis.

Examiner Tip: Mohr's salt is preferred over FeSO₄ for standard solutions in redox titrations because it is resistant to aerial oxidation (Fe²⁺ remains stable).

Top Examiner Traps & Pitfalls

Frequently tested misconceptions in Principles of Practical Chemistry & Salt Analysis

•Group II cations (Cu²⁺, Pb²⁺, etc.) precipitate with H₂S in ACIDIC medium (low [S²⁻]), whereas Group IV cations (Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺) require BASIC medium (high [S²⁻]).
•Chromyl chloride test fails for covalent halides (HgCl₂, AgCl, PbCl₂) and all bromides/iodides (no volatile red vapors formed).

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