Exam Master Review Sheet - Salt Analysis (JEE & NEET)

CHEMCA

EXAM MASTER REVIEW SHEET

Qualitative Inorganic Analysis

Comprehensive Logic & Tests for JEE Main, Advanced & NEET

1 Preliminary Dry Tests

Flame Test

Performed using a Pt wire and conc. HCl to convert salts into volatile chlorides.

Crimson Red: $Li^+$

Golden Yellow: $Na^+$

Violet/Lilac: $K^+$

Brick Red: $Ca^{2+}$

Crimson: $Sr^{2+}$

Apple Green: $Ba^{2+}$

Borax Bead Test

$Na_2B_4O_7 \cdot 10H_2O \xrightarrow{\Delta} 2NaBO_2 + B_2O_3$

Colored transition metal metaborates are formed.

Blue (Oxi/Red): $Co^{2+}$
Green (Oxi/Red): $Cr^{3+}$
Sky Blue (Oxi): $Cu^{2+}$ (Red opaque in Red. flame)
Yellow/Brown (Oxi): $Fe^{3+}$

2 Anionic Analysis (Acid Radicals)

Group I: Dilute $H_2SO_4$ or $HCl$

$CO_3^{2-}$ Brisk effervescence of colorless, odorless $CO_2$

$S^{2-}$ Rotten egg smell of $H_2S$ gas

$SO_3^{2-}$ Burning sulfur smell of $SO_2$

$NO_2^-$ Reddish-brown pungent fumes of $NO_2$

$CH_3COO^-$ Vinegar-like smell of acetic acid

Group II: Concentrated $H_2SO_4$

Anion	Observation with Conc. $H_2SO_4$	Confirmation
$Cl^-$	Pungent colorless fumes of $HCl$.	White dense fumes with $NH_4OH$ on a glass rod.
$Br^-$	Reddish-brown fumes of $Br_2$.	Fumes intensify on adding $MnO_2$ & heating.
$I^-$	Deep violet fumes of $I_2$.	Turns starch paper blue.
$NO_3^-$	Light brown fumes of $NO_2$.	Fumes intensely darken on adding Cu turnings.
$C_2O_4^{2-}$	Colorless gases ($CO + CO_2$).	$CO$ burns with a blue flame at the test tube mouth.

Independent Group (No Gas Evolved)

Sulphate ($SO_4^{2-}$): $BaCl_2$ Test

Aqueous solution + $BaCl_2(aq)$ $\rightarrow$ White ppt of $BaSO_4$.

The ppt is insoluble in conc. HCl or $HNO_3$.

Phosphate ($PO_4^{3-}$): Molybdate Test

Aqueous solution + Conc. $HNO_3$ + Ammonium Molybdate + $\Delta$ $\rightarrow$ Canary Yellow ppt.

Ppt is Ammonium phosphomolybdate: $(NH_4)_3[PMo_{12}O_{40}]$.

3 High-Yield Anion Confirmatory Tests

Chromyl Chloride Test ($Cl^-$)

Salt + solid $K_2Cr_2O_7$ + conc. $H_2SO_4$ $\xrightarrow{\Delta}$ Deep Red Vapours.

$CrO_2Cl_2 \uparrow$ (Chromyl Chloride)

Pass vapours into $NaOH(aq)$ $\rightarrow$ Yellow solution of $Na_2CrO_4$. Add acetic acid and lead acetate $\rightarrow$ Yellow ppt of $PbCrO_4$.

JEE Trap: Chlorides of Ag, Pb, Hg, Sn, Sb do NOT give this test!

Brown Ring Test ($NO_3^-$)

Aqueous salt solution + freshly prepared $FeSO_4$ solution. Add conc. $H_2SO_4$ carefully along the sides of the test tube.

A brown ring forms at the junction of the two liquids.

$[Fe(H_2O)_5(NO)]^{2+}$

Critical Detail: The oxidation state of Iron (Fe) in this complex is +1 (due to $NO^+$ ligand).

4 Cation Analysis (Basic Radicals)

The Guiding Principle

Precipitation occurs only when the Ionic Product (IP) exceeds the Solubility Product ($K_{sp}$). Group reagents are designed to control the concentration of precipitating ions (using the Common Ion Effect) so that cations precipitate selectively in a specific order.

Group	Cations	Group Reagent	Ppt & Principle
0	$NH_4^+$	$NaOH$, Heat	Evolution of $NH_3$ gas. Gives Brown ppt with Nessler's Reagent ($K_2HgI_4$).
I	$Pb^{2+}, Ag^+, Hg_2^{2+}$	Dilute $HCl$	Chlorides (White). Low $K_{sp}$ of these chlorides causes immediate precipitation. $PbCl_2$ dissolves in hot water.
II	$Cu^{2+}, Pb^{2+}, Hg^{2+}, Cd^{2+}, Bi^{3+}, As^{3+}, Sb^{3+}, Sn^{2+}$	$H_2S$ gas in presence of Dil. $HCl$	Sulphides. Dil. HCl suppresses ionization of $H_2S$ (Common ion effect), providing very low $[S^{2-}]$, sufficient only to precipitate Group II sulphides (which have extremely low $K_{sp}$).
III	$Fe^{3+}, Al^{3+}, Cr^{3+}$	Solid $NH_4Cl$ + $NH_4OH$ (excess)	Hydroxides. $NH_4Cl$ suppresses ionization of $NH_4OH$, lowering $[OH^-]$ to prevent precipitation of Group IV, V, VI hydroxides.
IV	$Zn^{2+}, Mn^{2+}, Co^{2+}, Ni^{2+}$	$H_2S$ gas in presence of $NH_4OH$	Sulphides. Basic medium removes $H^+$ from $H_2S$, increasing $[S^{2-}]$ high enough to exceed the moderate $K_{sp}$ of Group IV sulphides.
V	$Ba^{2+}, Sr^{2+}, Ca^{2+}$	$(NH_4)_2CO_3$ + $NH_4Cl$ + $NH_4OH$	Carbonates (White). $NH_4Cl$ prevents precipitation of $MgCO_3$ by lowering $[CO_3^{2-}]$.
VI	$Mg^{2+}$	$Na_2HPO_4$ + $NH_4OH$	White crystalline ppt of Magnesium ammonium phosphate ($MgNH_4PO_4$).

5 Specific Cation Confirmatory Tests

Copper ($Cu^{2+}$)

Add Potassium Ferrocyanide $K_4[Fe(CN)_6]$.

Chocolate Brown ppt: $Cu_2[Fe(CN)_6]$

Iron ($Fe^{3+}$)

1. With $K_4[Fe(CN)_6]$ $\to$ Prussian Blue ($Fe_4[Fe(CN)_6]_3$).

2. With $KSCN$ $\to$ Blood Red coloration ($[Fe(SCN)]^{2+}$).

Nickel ($Ni^{2+}$)

Add Dimethylglyoxime (DMG) in basic medium ($NH_4OH$).

Rosy Red / Cherry Red ppt: $[Ni(DMG)_2]$

Aluminum ($Al^{3+}$)

Lake Test: Add Blue Litmus solution, then $NH_4OH$ dropwise.

Blue gelatinous ppt floating in a colorless solution.

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Exam Master Review Sheet - Salt Analysis