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IITJEE CHEMISTRY: d/f-Block Elements & Qualitative Salt Analysis Visualizer

By

Ashish Kumar Bahekar

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APEX CLASS • IITJEE Inorganic Chemistry Lab

d/f-Block Elements & Qualitative Salt Analysis Visualizer

Master Lanthanide Contraction, KMnO₄ Titrations, Flame Tests, and The Brown Ring Complex!

🔬 Select a Transition Metal Concept:
Atomic Radius Group → 3d Series 4d Series Zr 5d Series Hf Atomic Twins! The Lanthanide Contraction • Normally, Size increases down a group. • But 4d and 5d transition metals have nearly IDENTICAL radii! Why? Extremely poor shielding by 4f electrons. Effective Nuclear Charge (Zeff) increases massively, shrinking the 5d atom’s radius. 1. d-d Transitions (Color) t2g eg hv (Light) Requires UNPAIRED d-electrons. (d⁰ and d¹⁰ are colorless!) 2. Spin-Only Magnetic Moment (μ) μ = √[ n (n + 2) ] BM • n = number of UNPAIRED electrons. • BM = Bohr Magneton. Shortcut: μ value always starts with ‘n’. n=1 → 1.73 | n=2 → 2.83 | n=3 → 3.87 | n=5 → 5.92 KMnO₄ Titrations: Oxidation State Drops & Color Changes Potassium Permanganate (Mn is in +7 state, Deep Purple) Acidic Medium (H⁺) Mn⁺⁷ → Mn²⁺ Purple → Colorless n-factor = 5 Neutral / Faintly Basic Mn⁺⁷ → Mn⁺⁴ (MnO₂) Purple → Brown Ppt n-factor = 3 Strongly Basic (OH⁻) Mn⁺⁷ → Mn⁺⁶ (MnO₄²⁻) Purple → Green n-factor = 1 🏆 JEE Mnemonic: “BAN 153” (Basic=1, Acidic=5, Neutral=3)! Potassium Dichromate: Chromate ⇌ Dichromate Equilibrium (pH Dependent) 2 CrO₄²⁻ Chromate (Yellow) Stable in Base (High pH) Add H⁺ (Acid) Add OH⁻ (Base) Cr₂O₇²⁻ + H₂O Dichromate (Orange) Stable in Acid (Low pH) Oxidation state of Cr is +6 in BOTH ions. This is NOT a redox reaction! ⚡ Oxidizing Action in Acid: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ (Green) + 7H₂O | n-factor = 6!
Mischmetal Alloy
95% Lanthanoid + 5% Fe
Used in bullets & lighter flints.
Catalytic Properties
Variable Ox. States
Allows them to form unstable intermediates.
Highest Ox. State
Osmium & Ruthenium (+8)
In compounds like OsO₄ and RuO₄.
Interstitial Compounds
H, C, N trapped in lattice
Makes metal harder, reduces malleability.
🧪 Select a Salt Analysis Concept to Visualize:
Cation Group Separation (Based on Ksp & Common Ion Effect) Group I Reagent: dil. HCl Ag⁺, Pb²⁺, Hg₂²⁺ Ppt as Chlorides (Low Ksp) Group II Reagent: H₂S in dil. HCl Cu²⁺, Cd²⁺, Bi³⁺, As³⁺ Ppt as Sulfides HCl suppresses [S²⁻]! Group III Reagent: NH₄OH + NH₄Cl Fe³⁺, Al³⁺, Cr³⁺ Ppt as Hydroxides NH₄Cl suppresses [OH⁻]! Group IV Reagent: H₂S in NH₄OH Zn²⁺, Mn²⁺, Co²⁺, Ni²⁺ Ppt as Sulfides NH₄OH increases [S²⁻]! 🎯 Group V (Ba, Sr, Ca) uses (NH₄)₂CO₃ in NH₄OH to ppt Carbonates. Group VI (Mg) uses Na₂HPO₄. Characteristic Flame Tests (Excitation of Valence Electrons) Brick Red Ca²⁺ Crimson Red Sr²⁺ Apple Green Ba²⁺ Blue-Green Cu²⁺ Golden Yellow Na⁺ Lilac K⁺ Electrons absorb heat, jump to higher energy levels, and emit characteristic visible light when dropping back. 1. The Brown Ring Test (For NO₃⁻) Brown Ring Formed Conc. H₂SO₄ FeSO₄(aq) + NO₃⁻ The Brown Ring Complex (Trap!) • Reaction: NO₃⁻ + 3Fe²⁺ + 4H⁺ → NO + 3Fe³⁺ + 2H₂O [Fe(H₂O)₆]²⁺ + NO → [Fe(H₂O)₅(NO)]²⁺ + H₂O [Fe(H₂O)₅(NO)]²⁺ 🚨 JEE Exception: Iron is in +1 state here! (NO acts as NO⁺, meaning Fe must be +1 to balance +2 overall) Chromyl Chloride Test (Confirmatory test for Cl⁻) Solid Salt + K₂Cr₂O₇ + H₂SO₄ Deep Red/Orange Vapors CrO₂Cl₂ (Chromyl Chloride) Contains Cr in +6 oxidation state! Pass vapors into NaOH(aq) → Solution turns Yellow (Na₂CrO₄ formed). Add Lead Acetate + Acetic Acid → Yellow Precipitate formed! Pb²⁺ + CrO₄²⁻ → PbCrO₄(s) ↓ (Lead Chromate) 🚨 Limitation: F⁻, Br⁻, I⁻ do NOT give this test! Also, covalent chlorides (HgCl₂, AgCl) do not respond well.
Nessler’s Reagent
K₂[HgI₄] in KOH
Detects NH₄⁺. Forms Brown ppt (Iodide of Millon’s base).
Dimethylglyoxime (DMG)
Rosy Red ppt with Ni²⁺
Forms square planar complex [Ni(DMG)₂].
Borax Bead Test (Co)
Deep Blue Bead
Formation of Cobalt Metaborate Co(BO₂)₂.
Sulfate (SO₄²⁻) Test
BaCl₂ yields White Ppt
BaSO₄ is insoluble even in conc. HCl.
🔥 High-Yield Amphoteric Trick:
In Group III, when separating Fe³⁺, Al³⁺, and Cr³⁺, adding excess NaOH + H₂O₂ causes Al³⁺ to dissolve as [Al(OH)₄]⁻ (colorless) and Cr³⁺ to oxidize and dissolve as CrO₄²⁻ (yellow). Only Fe³⁺ remains behind as a reddish-brown precipitate of Fe(OH)₃!
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