Last Updated: October 2026 for NEET 2027 • Chemistry Bureau
"Fk that salt analysis kiya ni tha... wtf I am doing with myself this is my 2nd drop 🙂"
This quote from r/Neet_india came from a dropper stepping out of a Sunday mock test. When NTA formally introduced Practical Chemistry into the NEET syllabus, coaching institutes handed out 80-page lab manuals. Droppers panicked, believing that on top of D-Block and P-Block, they now had to memorize an entire laboratory manual.
Zameeni sach yeh hai: Practical Chemistry in NEET is simply applied D-Block and Chemical Equilibrium. NEET does not test obscure lab maneuvers. Questions focus strictly on systematic cation separation across Groups 0 to VI, their designated group reagents, precipitate colours, and high-frequency confirmatory tests.
The Seedha Faisla / Ruling: Practical Chemistry in NEET tests systematic qualitative salt analysis across Groups 0 through VI governed by Solubility Product ($K_{sp}$) and the Common Ion Effect. Group 0 uses NaOH (heat) to liberate $NH_3$. Group I uses dilute $HCl$ ($Pb^{2+}$ white precipitate). Group II uses $H_2S$ in dilute $HCl$ ($Cu^{2+}, Pb^{2+}, Bi^{3+}, As^{3+}$). Group III uses $NH_4OH$ with solid $NH_4Cl$ ($Fe^{3+}, Al^{3+}, Cr^{3+}$). Group IV uses $H_2S$ in alkaline $NH_4OH$ ($Zn^{2+}, Mn^{2+}, Co^{2+}, Ni^{2+}$). Group V uses $(NH_4)_2CO_3$ ($Ba^{2+}, Sr^{2+}, Ca^{2+}$). Group VI confirms $Mg^{2+}$ with $Na_2HPO_4$. Mastering this 6-group reagent sequence secures 4 to 8 guaranteed marks.
What Are the 6 Group Reagents in NEET Salt Analysis?
In qualitative analysis, cations are precipitated systematically in increasing order of their solubility product ($K_{sp}$). Each group requires a specific Group Reagent:
| Cation Group | Cations Included | Group Reagent | Precipitate Formed & Colour | Ksp & Chemical Equilibrium Traps |
|---|---|---|---|---|
| Group 0 | $NH_4^+$ (Ammonium) | $NaOH$ (Heat) | $NH_3$ gas evolves | Turns Nessler's reagent brown ($[HgO \cdot Hg(NH_2)I]$) |
| Group I | $Pb^{2+}$ | Dilute $HCl$ | $PbCl_2$ (White precipitate) | Soluble in hot water; recrystallizes as needles on cooling |
| Group II | $Cu^{2+}, Pb^{2+}, Bi^{3+}, As^{3+}$ | $H_2S$ in dilute $HCl$ | $CuS$ (Black), $As_2S_3$ (Yellow) | Acidic medium keeps $[S^{2-}]$ low via common ion effect |
| Group III | $Fe^{3+}, Al^{3+}, Cr^{3+}$ | $NH_4OH$ in solid $NH_4Cl$ | $Fe(OH)_3$ (Red-Brown), $Al(OH)_3$ (White) | $NH_4^+$ suppresses $[OH^-]$ so Group IV/V do not precipitate |
| Group IV | $Zn^{2+}, Mn^{2+}, Co^{2+}, Ni^{2+}$ | $H_2S$ in $NH_4OH$ (Basic) | $ZnS$ (White), $MnS$ (Buff / Flesh), $NiS$ (Black) | Basic medium increases $[S^{2-}]$ to exceed higher $K_{sp}$ |
| Group V | $Ba^{2+}, Sr^{2+}, Ca^{2+}$ | $(NH_4)_2CO_3$ in $NH_4OH$ | $BaCO_3, SrCO_3, CaCO_3$ (White) | Conducted in presence of $NH_4Cl$ to keep $Mg^{2+}$ soluble |
| Group VI | $Mg^{2+}$ | $Na_2HPO_4$ with $NH_4OH$ | $Mg(NH_4)PO_4$ (White crystalline) | Confirmatory test for magnesium cation |
Why Is Dilute HCl Added Before H2S in Group II?
NTA does not merely ask for precipitate colours; questions test the underlying chemical equilibrium:
- Why is dilute $HCl$ added before $H_2S$ in Group II?
$HCl$ is a strong electrolyte that completely ionizes into $H^+$ and $Cl^-$. The excess $H^+$ ions suppress the ionization of the weak diprotic acid $H_2S$ via the Common Ion Effect:
$$H_2S \rightleftharpoons 2H^+ + S^{2-}$$
This keeps the sulfide ion concentration $[S^{2-}]$ extremely low. It is just high enough to exceed the very low solubility product ($K_{sp}$) of Group II sulfides ($CuS, PbS$), but strictly below the higher $K_{sp}$ of Group IV sulfides ($ZnS, NiS$), preventing premature precipitation.
- Why is solid $NH_4Cl$ added before $NH_4OH$ in Group III?
Solid $NH_4Cl$ furnishes high $[NH_4^+]$, which shifts the equilibrium of weak base $NH_4OH$ backward:
$$NH_4OH \rightleftharpoons NH_4^+ + OH^-$$
This keeps $[OH^-]$ low, so only the highly insoluble hydroxides of $Fe^{3+}, Al^{3+}, Cr^{3+}$ precipitate, leaving Group IV, V, and VI cations safely in the filtrate.
Which 4 Confirmatory & Flame Tests Are Most Asked in NEET?
1. Brown Ring Test for Nitrate ($NO_3^-$)
Freshly prepared $FeSO_4$ is added to the salt solution, followed by concentrated $H_2SO_4$ slowly along the inner sides of the test tube. A dark brown ring forms at the liquid junction.
- Formula of the Brown Ring Complex: $[Fe(H_2O)_5(NO)]SO_4$
- Oxidation State of Iron: Iron is in the $+1$ oxidation state ($Fe^+$, with $NO^+$ nitrosonium ligand), giving 3 unpaired electrons ($\mu = 3.87\text{ BM}$).
2. Lead Chromate Test for Lead ($Pb^{2+}$)
The salt solution treated with potassium chromate ($K_2CrO_4$) yields a bright yellow precipitate of lead chromate ($PbCrO_4$). This precipitate is soluble in excess $NaOH$ forming soluble sodium plumbite.
3. Flame Test Colours Reference
When concentrated $HCl$ paste of the salt is placed on a platinum wire in a non-luminous Bunsen flame:
- Calcium ($Ca^{2+}$): Brick Red flame
- Strontium ($Sr^{2+}$): Crimson Red flame
- Barium ($Ba^{2+}$): Apple Green flame
- Copper ($Cu^{2+}$): Blue-Green flame
- Sodium ($Na^+$): Persistent Golden Yellow flame
- Potassium ($K^+$): Lilac / Violet flame
Related reading from the Chemistry Bureau:
- Inorganic Chemistry for NEET: 2027 NCERT Roadmap
- The P-Block Dilemma: Exactly What Trends Are IN vs Compounds Dead
- Chemical Bonding & Coordination Compounds: The 8 Questions Carrying 50% Marks
- D & F Block NCERT Line-by-Line: The 5 Colour & Oxidation State Tables You Must Mug Up
- Inorganic NCERT Reading Protocol: Why Making 10-Page Short Notes Fails