Solutions – JEE Mains Chemistry
1. Concentration Units
- Molality (m): Moles of solute per kg of solvent.
- Molarity (M): Moles of solute per litre of solution.
- Mole Fraction: Ratio of moles of a component to total moles in solution.
- Percentage: By mass or volume – amount of solute per 100 parts of solution.
2. Vapour Pressure of Solutions and Raoult’s Law
- Raoult’s Law: Partial vapour pressure of a component is proportional to its mole fraction.
- Ideal Solutions: Follow Raoult’s Law at all concentrations and have ΔH_mix = 0, ΔV_mix = 0.
- Non-Ideal Solutions: Show positive or negative deviations from Raoult’s Law.
- Vapour Pressure-Composition Plots: Graphical representation helps identify ideal and non-ideal behavior.
3. Colligative Properties of Dilute Solutions
- Relative Lowering of Vapour Pressure: Proportional to mole fraction of solute.
- Depression of Freezing Point: ΔT_f = K_f · m.
- Elevation of Boiling Point: ΔT_b = K_b · m.
- Osmotic Pressure (π): π = CRT (C is molar concentration, R is gas constant, T is temperature).
4. Determination of Molecular Mass
Colligative properties are used to calculate molar masses of solutes, especially in dilute solutions.
5. Abnormal Molar Mass and van’t Hoff Factor
- Abnormal Molar Mass: Occurs due to association or dissociation of solute in solution.
- van’t Hoff Factor (i): Accounts for actual number of particles in solution. Adjusts colligative property formulas.
- Significance: Helps identify ionization and aggregation in electrolytes and solutes.