Solutions and Colligative Properties

Vocabulary flashcards covering key terms from lecture notes on solutions, Raoult’s law, colligative properties, and related concepts.

Solution

A homogeneous mixture of two or more substances (solute + solvent).

Solvent

The component present in a solution in relatively large proportion; determines the physical state of the solution.

Solute

The component present in a solution in relatively small proportion; can be one or more in a given solvent.

Binary Solution

A solution containing two components (one solvent and one solute).

Ternary Solution

A solution containing three components.

Quaternary Solution

A solution containing four components.

Gaseous Solution

A solution in which the solvent is a gas; solute may be solid, liquid, or gas.

Liquid Solution

A solution in which the solvent is a liquid.

Solid Solution

A solution in which the solvent is a solid (e.g., copper dissolved in gold).

Henry’s Law

At constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the solution (P = k_H · x).

Henry’s Law Constant (k_H)

The proportionality constant in Henry’s Law; specific to each gas–solvent pair and temperature.

Limitation of Henry’s Law

Valid only at low gas pressures and moderate temperatures.

Carbonation (Application of Henry’s Law)

CO₂ is dissolved in soft drinks under high pressure to increase solubility.

Mass Percentage (w/w %)

(Mass of solute / Total mass of solution) × 100.

Volume Percentage (v/v %)

(Volume of solute / Total volume of solution) × 100.

Mass by Volume Percentage (w/v %)

(Mass of solute / Volume of solution) × 100.

Parts per Million (ppm)

(Number of parts of component / Total parts of solution) × 10⁶; used for very dilute solutions.

Mole Fraction (x)

Ratio of moles of one component to total moles of all components in the solution.

Molarity (M)

Moles of solute per litre of solution (mol · L⁻¹); temperature dependent.

Molality (m)

Moles of solute per kilogram of solvent (mol · kg⁻¹); temperature independent.

Vapour Pressure

Pressure exerted by vapour in equilibrium with its liquid at a given temperature.

Raoult’s Law (Volatile Components)

Partial vapour pressure of each component equals the product of its mole fraction in solution and its vapour pressure in pure state (PA = PA° x_A).

Raoult’s Law (Non-volatile Solute)

Relative lowering of vapour pressure equals mole fraction of non-volatile solute.

Ideal Solution

A solution that obeys Raoult’s Law over the entire composition range and shows ΔHmix = 0 and ΔVmix = 0.

Conditions for Ideal Solutions

(i) Similar intermolecular forces between A–A, B–B, and A–B; (ii) Components have similar structure and polarity.

Non-Ideal Solution

A solution that deviates from Raoult’s Law; shows either positive or negative deviation.

Positive Deviation

Observed vapour pressure is greater than predicted; A–B interactions weaker than A–A or B–B (ΔHmix > 0, ΔVmix > 0).

Negative Deviation

Observed vapour pressure is lower than predicted; A–B interactions stronger than A–A or B–B (ΔHmix < 0, ΔVmix < 0).

Azeotrope

A constant-boiling binary mixture whose vapour has the same composition as the liquid; cannot be separated by fractional distillation.

Minimum-Boiling Azeotrope

Azeotrope with lower boiling point than either component; arises from positive deviation (e.g., 95% ethanol–water).

Maximum-Boiling Azeotrope

Azeotrope with higher boiling point than either component; arises from negative deviation (e.g., 68% HNO₃–H₂O).

Colligative Property

Property that depends only on the number of solute particles, not their nature (e.g., RLVP, ΔTb, ΔTf, osmotic pressure).

Relative Lowering of Vapour Pressure (RLVP)

(P° – P) / P°; proportional to mole fraction of solute in dilute solutions.

Elevation of Boiling Point (ΔT_b)

Increase in boiling point when a non-volatile solute is added; ΔTb = Kb·m.

Ebullioscopic Constant (K_b)

Molal elevation constant; ΔT_b when solute molality is 1 mol · kg⁻¹.

Depression of Freezing Point (ΔT_f)

Decrease in freezing point when a solute is added; ΔTf = Kf·m.

Cryoscopic Constant (K_f)

Molal depression constant; ΔT_f when solute molality is 1 mol · kg⁻¹.

Osmosis

Spontaneous flow of solvent through a semipermeable membrane from pure solvent to solution side.

Semipermeable Membrane (SPM)

A membrane that allows only solvent molecules (not solute) to pass through.

Osmotic Pressure (π)

External pressure required to stop osmosis; for dilute solutions π = C R T = (n/V) R T.

Reverse Osmosis

Process where pressure greater than osmotic pressure is applied to the solution side, forcing solvent to flow out; used in desalination.

Abnormal Molar Mass

Molar mass calculated from colligative properties differing from normal due to solute association or dissociation.

Association (of Solute)

Combination of solute molecules (e.g., dimerization) decreasing particle number and colligative properties, giving higher apparent molar mass.

Dissociation (of Solute)

Splitting of solute into ions increasing particle number and colligative properties, giving lower apparent molar mass.

van’t Hoff Factor (i)

Ratio of observed colligative property to the value expected for nonelectrolyte; accounts for association/dissociation (i = observed molar mass / normal molar mass).

Relation of i to Degree of Dissociation (α)

For electrolyte giving n particles, i = 1 + α(n – 1).