Pattern 1: Colligative Property Calculations (Every Year)

Format: Given mass of solute, mass of solvent, asked for $\Delta Tb$ or $\Delta Tf$. Steps: (1) Find moles of solute → (2) Find molality = mol/kg solvent → (3) $\Delta T$ = i × K × m. Watch for: Is solute an electrolyte? If yes, apply i. Are units kg or g for solvent? Convert to kg.

Sample PYQ (NEET 2019): 30 g unknown dissolved in 500 g water, $\Delta Tb$ = 0.52°C. Find M. Answer: M = Kb × w_{2} × 1000 / ($\Delta Tb$ × w_{1}) = 0.52 × 30000 / (0.52 × 500) = 60 g/mol.

Pattern 2: Van't Hoff Factor Numericals (High Frequency)

Format: Observed $\Delta Tf$ given, expected $\Delta Tf$ calculated, find i → find α. Steps: (1) i = $\Delta Tf$(obs) / $\Delta Tf$(expected) → (2) Use i = 1 + (n−1)α for dissociation OR i = 1 − α/2 for dimerization.

Most tested systems:

• Acetic acid in benzene (dimerization): i < 1, α = 2(1−i)
• NaCl, KCl in water (dissociation): i = 1 + α (n=2)
• $CaCl_{2}$, $K_{2}SO_{4}$ in water (n=3): i = 1 + 2α

Pattern 3: Ideal vs Non-Ideal (Identification Questions)

Frequently asked pairs:

• Benzene + toluene → IDEAL ✓
• Ethanol + water → Positive deviation, min. boiling azeotrope ✓
• $CHCl_{3}$ + acetone → Negative deviation, max. boiling azeotrope ✓
• HCl + water → Negative deviation, max. boiling azeotrope ✓
• Acetone + $CS_{2}$ → Positive deviation ✓

Pattern 4: Comparing Colligative Effects (Ranking Questions)

Format: Which 0.1 m solution has highest/lowest boiling/freezing point? Method: Rank by i value. $AlCl_{3}$ (i=4) > $CaCl_{2}$ (i=3) > NaCl (i=2) > Glucose (i=1). Highest boiling point = Highest $\Delta Tb$ = Highest i = $AlCl_{3}$ Lowest freezing point = Highest $\Delta Tf$ = Highest i = $AlCl_{3}$

Pattern 5: Osmotic Pressure for Molar Mass

Format: Protein/polymer dissolved in water, osmotic pressure given, find molar mass. Formula: M = w_{2}RT / (π × V). Key: use T in Kelvin, π in atm, V in litres.

NEET Year-wise Trend