Concept: Concentration terms measure the proportion of solute in a solution.
Solutions are composed of solvents (represented as 'A') and solutes (represented as 'B').
Molarity (M)
Definition: Number of moles of solute in 1 liter of solution.
Formula: [ \text{Molarity} (M) = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} ]
Units: moles per liter (mol/L or M).
Molality (m)
Definition: Number of moles of solute in 1 kg of solvent.
Formula: [ \text{Molality} (m) = \frac{\text{Number of moles of solute}}{\text{Mass of solvent in kg}} ]
Units: moles per kilogram (mol/kg or m).
Mole Fraction (χ)
Definition: Ratio of the moles of a component to the total moles in the solution.
Formula (Solvent): [ χ_A = \frac{\text{moles of solvent}}{\text{total moles}} ]
Formula (Solute): [ χ_B = \frac{\text{moles of solute}}{\text{total moles}} ]
Property: Sum of mole fractions in a binary solution is 1.
Mass Percentage (% mass)
Formula: [ \text{Mass Percentage} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100 ]
Volume Percentage (% vol)
Formula: [ \text{Volume Percentage} = \frac{\text{Volume of solute}}{\text{Volume of solution}} \times 100 ]
Strength
Similar to mass percentage but involves volume of solution.
Normality (N)
Similar to molarity but uses equivalents.
Units: equivalents per liter (eq/L or N).
Relationship between Molarity, Molality, and Density
Important for problem-solving when two of the three terms are given: molarity (M), molality (m), and density (ρ).
Relation: Utilize given equations to find the unknown term.
Henry's Law
States that the amount of gas dissolved in a liquid is proportional to its partial pressure above the liquid.
Vapor Pressure
Definition: Pressure exerted by a vapor in equilibrium with its liquid or solid form.
Affected by temperature and the nature of the liquid.
Decreases when a non-volatile solute is added to a volatile solvent (Raoult’s Law).
Raoult’s Law
Vapor pressure of a solution is directly proportional to the mole fraction of the solvent.
For volatile components: [ P_A = P^0_A χ_A ], where (P^0_A) is the vapor pressure of the pure solvent.
Non-Ideal Solutions
Show deviations from Raoult’s Law (positive or negative deviations).
Positive deviation: Weaker intermolecular forces in solution, higher vapor pressure.
Negative deviation: Stronger intermolecular forces in solution, lower vapor pressure.
Azeotropes
Mixtures with the same composition in liquid and vapor phases, boiling at a constant temperature.
Types
Maximum boiling azeotropes (e.g., HCl-water)
Minimum boiling azeotropes (e.g., Ethanol-water)
Colligative Properties
Properties dependent on the number of solute particles, not the nature.
Examples:
Relative lowering of vapor pressure
Elevation of boiling point
Depression of freezing point
Osmotic pressure
Elevation of Boiling Point
Formula: [ ΔT_b = K_b , m , i ] (molal boiling point elevation constant).
Depression of Freezing Point
Formula: [ ΔT_f = K_f , m , i ] (cryoscopic constant).
Osmotic Pressure
Formula: [ π = C , R , T ]
Application in finding molar mass from colligative properties.
Van’t Hoff Factor (i)
Adjustment for dissociation or association of solutes.
Used to correct colligative properties: [ i = \frac{\text{observed colligative property}}{\text{calculated colligative property assuming no dissociation/association}} ]
Example Calculations
Various scenarios and practical problems solved using above principles.
Always check units and consistency in calculations.
Practice Questions
On increasing altitude, vapor pressure remains the same if temperature is constant.
Ideal vs. non-ideal solutions and their behavior.
Examples and problem-solving techniques for colligative properties.
Application of Henry’s and Raoult’s laws in real-life scenarios.