Solutions

1. Types of Solutions

A Solution is a homogeneous mixture of two or more chemically non-reacting substances. In a binary solution, the component present in larger quantity is the Solvent, and the other is the Solute.

Type of Solution	Solute	Solvent	Common Example
Gaseous	Gas	Gas	Mixture of Oxygen and Nitrogen
	Liquid	Gas	Chloroform mixed with Nitrogen gas
	Solid	Gas	Camphor in Nitrogen gas
Liquid	Gas	Liquid	Oxygen dissolved in water
	Liquid	Liquid	Ethanol dissolved in water
	Solid	Liquid	Glucose dissolved in water
Solid	Gas	Solid	Solution of Hydrogen in Palladium
	Liquid	Solid	Amalgam of Mercury with Sodium
	Solid	Solid	Copper dissolved in Gold (Alloys)

2. Expressing Concentration

Concentration describes the amount of solute present in a given amount of solvent or solution.

Molarity (M) = Moles of Solute / Volume of Solution (L)

Unit: mol/L. Temperature dependent (volume changes with T).

Molality (m) = Moles of Solute / Mass of Solvent (kg)

Unit: mol/kg. Temperature independent (mass doesn't change with T).

Mole Fraction (x_A) = n_A / (n_A + n_B)

Dimensionless. x_A + x_B = 1.

IAT Quick Tip: Density Connection

Relationship between Molarity (M) and Molality (m):

1/m = (d/M) - (M_solute/1000)

Where d is density in g/mL and M_solute is molar mass of solute.

3. Solubility & Henry's Law

Solubility is the maximum amount of solute that can be dissolved in a specific amount of solvent at a specified temperature.

Factors Affecting Solubility

Nature of Solute/Solvent: "Like dissolves like."
Temperature: Usually solubility of solids increases with T (Endothermic), while solubility of gases decreases with T.
Pressure: No effect on solids/liquids, but huge effect on gases (Henry's Law).

p = K_H · x

Henry's Law: Partial pressure (p) is proportional to mole fraction (x) in solution.

K_H Insights

Higher K_H value at a given pressure means Lower Solubility. K_H increases with temperature, which is why aquatic species are more comfortable in cold water (more O₂ dissolved).

4. Vapour Pressure & Raoult's Law

Vapour pressure depends on the nature of the liquid and the temperature.

P_total = P_A^°x_A + P_B^°x_B

Raoult's Law for binary solutions of volatile liquids.

Non-Volatile Solutes

Addition of a non-volatile solute lowers the vapour pressure of the solvent because solute particles occupy surface sites, reducing the rate of evaporation.

P_soln = P_solvent^° · x_solvent

5. Ideal vs. Non-Ideal Solutions

Ideal Solutions: Molecules of A and B have similar sizes and polarities. Interactions A-B ≈ A-A or B-B.

Property	Ideal Solution	Positive Deviation	Negative Deviation
Raoult's Law	Obeyed at all conc.	P_obs > P_calc	P_obs < P_calc
Interactions	A-B = A-A, B-B	A-B < A-A, B-B	A-B > A-A, B-B
ΔH_mix	ΔH_mix = 0	ΔH_mix > 0 (Endo)	ΔH_mix < 0 (Exo)
ΔV_mix	ΔV_mix = 0	ΔV_mix > 0	ΔV_mix < 0
Examples	Benzene + Toluene	Acetone + Ethanol	Chloroform + Acetone

Azeotropes (Constant Boiling Mixtures)

Minimum Boiling Azeotrope: Formed by large Positive deviation. Boiling point is lower than either component.
Maximum Boiling Azeotrope: Formed by large Negative deviation. Boiling point is higher than either component.

6. Colligative Properties

Properties that depend ONLY on the number of solute particles, irrespective of their nature.

RLVP: (P°_A - P_s) / P°_A = i · x_B

Relative Lowering of Vapour Pressure.

ΔT_b = i · K_b · m

Boiling Point Elevation. K_b (Molal elevation constant) depends on solvent nature.

ΔT_f = i · K_f · m

Freezing Point Depression. K_f (Cryoscopic constant).

π = i · CRT

Osmotic Pressure. π is in Pascals or atm based on R value.

7. Abnormal Molar Masses & Van't Hoff Factor

When solutes dissociate or associate in solution, the number of particles changes, leading to abnormal molar mass values calculated from colligative properties.

i = Observed Colligative Property / Calculated Property

i = Normal Molar Mass / Abnormal Molar Mass

Calculated i values

Dissociation (e.g., NaCl): i = 1 + (n-1)α. i > 1.
Association (e.g., Acetic acid in Benzene): i = 1 + (1/n - 1)α. i < 1.

Note: Solute molar mass is inversely proportional to the colligative property.

7. IAT Exam Focus Points

Colligative Proportionality:

Remember that ALL colligative properties are directly proportional to i × m.

Azeotrope Logic:

Positive deviation azeotropes have a minimum boiling point; negative deviation azeotropes have a maximum boiling point.

Osmotic Pressure:

Most frequent calculation. Remember: convert T to Kelvin and V to Liters.

8. Quick Revision Flashcards

Henry's Law constant (K_H) & Temperature

K_H increases with Temperature, resulting in decreased solubility of gases.

Van't Hoff factor (i) for Al₂(SO₄)₃

i = 5 (assuming 100% dissociation into 2Al³⁺ and 3SO₄^2-).

Minimum Boiling Azeotrope

Formed by solutions showing large Positive Deviation from Raoult's Law.

Negative Deviation Interactions

A-B interactions are STRONGER than A-A and B-B interactions.

9. Practice Mock Test

Ready to test your knowledge?

Take a quick 15-question assessment specifically designed for Solutions. Challenge yourself with IAT-level questions.

Start Practice Mock

End of Chapter