| Question | Answer |
|---|---|
| Define Molarity | Moles of solute per litre of solution (mol/L); temperature-dependent |
| Define Molality | Moles of solute per kilogram of solvent (mol/kg); temperature-independent |
| Define Mole Fraction | nᵢ / n_total (dimensionless); sum of all mole fractions in a mixture = 1 |
| Define Normality | Equivalents of solute per litre of solution (eq/L); depends on n-factor and reaction type |
| Define ppm | mg of solute per kg of solution (= mg/L for dilute aqueous solutions) |
| Why is molality preferred for colligative properties? | It is temperature-independent (uses mass of solvent), so boiling point elevation and freezing point depression calculations remain consistent |
| What is the n-factor of in neutralisation? | 2 (donates 2 ); equivalent weight = 98/2 = 49 g/eq |
| When does Normality = Molarity? | When n-factor = 1 (e.g., HCl, NaOH in acid-base reactions) |
| How is Normality related to Molarity? | N = M × n-factor |
| Express 0.5 M NaOH as molality if d = 1.02 g/mL | Mass of NaOH in 1 L = 20 g; mass solution = 1020 g; solvent = 1000 g = 1 kg; m = 0.5 mol/kg |
Summary: Each concentration term suits a specific context: Molarity for lab titrations, Molality for colligative properties, Normality for equivalent-based reactions, and ppm for trace-level solutions. The critical NEET skill is converting between these using density and molar mass.