Exam Master Review Sheet - Purification & Analysis

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EXAM MASTER FORMULA SHEET

Purification & Characterization

Strategic Lab Techniques for JEE Main, Advanced & NEET

1. Physical Purification Methods

Sublimation

Separation of a sublimable solid from non-sublimable impurities (Solid $\to$ Vapor without liquid phase).

Examples: Camphor, Naphthalene, Anthracene, Benzoic Acid.

Crystallization

Based on the difference in solubilities of the compound and the impurities in a suitable hot solvent.

*Impurity should be either insoluble in the hot solvent or highly soluble in the cold solvent.*

Differential Extraction

Extracting an organic compound from an aqueous solution using an immiscible organic solvent in which the compound is highly soluble.

Governed by Partition Coefficient ($K_D$)

2. Distillation Techniques

Method	Principle / Criteria	Common Examples
Simple Distillation	Difference in Boiling Point is large ($> 25$ K). Liquids must be stable at their B.P.	Chloroform (334K) & Aniline (457K); Ether & Toluene
Fractional Distillation	Difference in B.P. is small ($< 25$ K). Uses a fractionating column to provide many condensation surfaces.	Acetone & Methyl Alcohol; Crude Oil fractions
Vacuum Distillation (Under reduced pressure)	Used for liquids that decompose at or below their normal B.P. Lowering pressure lowers the B.P.	Glycerol from spent-lye; Concentration of Sugarcane juice
Steam Distillation	For compounds that are steam-volatile and immiscible with water. $P_{\text{total}} = P_{\text{water}} + P_{\text{organic}}$	Aniline - Water mixture; o-Nitrophenol; Essential Oils

Steam Distillation Numerical Formula:

\[ \frac{w_1}{w_2} = \frac{p_1 M_1}{p_2 M_2} \]

Where $w$ = mass, $p$ = vapor pressure, $M$ = molar mass ($1$ = organic compound, $2$ = water).

3. Chromatography

Based on the difference in movement of components in a mixture through a stationary phase under the influence of a mobile phase.

Adsorption Chromatography

Based on differential adsorption of components on a solid adsorbent (like Silica gel or Alumina).

• Column Chromatography (CC)
• Thin Layer Chromatography (TLC)

Partition Chromatography

Based on continuous differential partitioning of components between a stationary liquid phase and a mobile phase.

• Paper Chromatography (Water trapped in paper acts as stationary phase)

Retardation Factor ($R_f$):

\[ R_f = \frac{\text{Distance moved by the substance from baseline}}{\text{Distance moved by the solvent from baseline}} \]

$0 \le R_f \le 1$. High $R_f$ $\implies$ lower adsorption on stationary phase.

4. Qualitative Analysis (Lassaigne's Test)

Principle of Sodium Fusion:

Covalent bonds in organic compounds are converted into ionic bonds by fusing with Sodium metal.

$Na + C + N \to NaCN$
$2Na + S \to Na_2S$
$Na + X \to NaX$

Element	Reagents Added to Extract	Observation / Chemical Complex
Nitrogen ($N$)	Fresh $FeSO_4$ $\to$ Boil $\to$ cool $\to$ add conc. $H_2SO_4$	Prussian Blue color $Fe_4[Fe(CN)_6]_3 \cdot xH_2O$
Sulfur ($S$)	Sodium Nitroprusside	Deep Violet color $[Fe(CN)_5NOS]^{4-}$
Both N + S	$FeCl_3$	Blood Red color $[Fe(SCN)]^{2+}$
Halogens ($X$)	Boil with $HNO_3$ (to expel $HCN/H_2S$) $\to$ add $AgNO_3$	$Cl$: White ppt ($AgCl$, sol in $NH_4OH$) $Br$: Pale Yellow ppt ($AgBr$, sparingly sol) $I$: Yellow ppt ($AgI$, insol in $NH_4OH$)
Phosphorus ($P$)	Oxidize with $Na_2O_2$ $\to$ boil with $HNO_3$ $\to$ add Ammonium Molybdate	Yellow precipitate $(NH_4)_3PO_4 \cdot 12MoO_3$

Exceptions: Compounds like Hydrazine ($NH_2NH_2$) and Hydroxylamine ($NH_2OH$) do not contain Carbon, hence they cannot form $NaCN$ and fail the Lassaigne's test for Nitrogen. Diazonium salts lose $N_2$ gas upon heating and also fail the test.

5. Quantitative Estimation Master Formulas

Liebig's Method (C & H)

Compound heated with $CuO$. C oxidizes to $CO_2$, H to $H_2O$.

\[ \%C = \frac{12}{44} \times \frac{w_{CO_2}}{w_{\text{org}}} \times 100 \] \[ \%H = \frac{2}{18} \times \frac{w_{H_2O}}{w_{\text{org}}} \times 100 \]

Carius Method (X, S, P)

Heated with fuming $HNO_3$ + $AgNO_3$ (for X) or $BaCl_2$ (for S).

\[ \%X = \frac{\text{At. mass of X}}{\text{Mol. mass of } AgX} \times \frac{w_{AgX}}{w_{\text{org}}} \times 100 \] \[ \%S = \frac{32}{233} \times \frac{w_{BaSO_4}}{w_{\text{org}}} \times 100 \]

Nitrogen Estimation (Crucial)

Dumas Method:

Compound heated with $CuO$ in $CO_2$ atm. N collected as $N_2$ gas.

\[ \%N = \frac{28}{22400} \times \frac{V_{N_2 \text{ at STP}}}{w_{\text{org}}} \times 100 \]

$V$ must be in mL.

Kjeldahl's Method:

Compound digested with $H_2SO_4$, N converted to $(NH_4)_2SO_4$.

\[ \%N = \frac{1.4 \times N \times V}{w_{\text{org}}} \]

*Fails for: Nitro, Azo, and Ring Nitrogen (e.g., Pyridine) because N does not convert to Ammonium sulfate.*

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