Introduction
A solution is a homogeneous mixture of two or more components. This chapter deals with concentration, solubility, colligative properties, and their applications.
👉 Core Idea: Properties of solutions depend on the number and nature of particles present.
1. Types of Solutions
Based on Physical State
| Solute | Solvent | Example |
|---|---|---|
| Gas | Gas | Air |
| Liquid | Liquid | Alcohol in water |
| Solid | Liquid | Salt in water |
2. Concentration of Solutions
(A) Mass Percentage
Mass % = (Mass of solute / Mass of solution) × 100
(B) Volume Percentage
Volume % = (Volume of solute / Volume of solution) × 100
(C) Molarity (M)
M = n / V
Where:
- n = moles
- V = volume (L)
(D) Molality (m)
m = n / mass of solvent (kg)
(E) Mole Fraction (χ)
χ = moles of component / total moles
Concept Clarity
👉 WHY molality preferred?
Because it is independent of temperature.
3. Solubility
Definition
Maximum amount of solute dissolved in solvent at given temperature.
Henry’s Law (Very Important)
Statement
Solubility of gas is proportional to pressure.
Formula
p = kH x
Concept Clarity
👉 WHY cold drinks fizz when opened?
Because pressure decreases → gas escapes.
4. Vapour Pressure
Raoult’s Law
Statement
Vapour pressure of solution is proportional to mole fraction of solvent.
Formula
P = P° x solvent
For Binary Solutions
P_total = P₁°x₁ + P₂°x₂
5. Ideal and Non-Ideal Solutions
Ideal Solution
- Obey Raoult’s law
- No heat change
Non-Ideal Solution
- Do not obey Raoult’s law
Types
- Positive deviation
- Negative deviation
6. Colligative Properties (Very Important)
Properties depending only on number of particles.
(A) Relative Lowering of Vapour Pressure
ΔP / P° = χsolute
(B) Elevation in Boiling Point
ΔTb = Kb m
(C) Depression in Freezing Point
ΔTf = Kf m
(D) Osmotic Pressure
π = CRT
Concept Clarity
👉 WHY colligative properties important?
They help determine molar mass.
7. Van’t Hoff Factor (i)
Definition
Accounts for association/dissociation of solute.
Formula
i = observed value / calculated value
Examples
- NaCl → i ≈ 2
- Glucose → i = 1
8. Abnormal Molar Mass
Occurs due to:
- Association
- Dissociation
9. Important Numericals
Numerical 1
Find molarity if 1 mole solute in 1 L solution
M = 1 M
Numerical 2
Find molality if 1 mole in 1 kg solvent
m = 1 m
Numerical 3
Find ΔTb if Kb = 0.5, m = 2
ΔTb = 1 K
Numerical 4
Find osmotic pressure
π = CRT
Numerical 5 (JEE Level)
Calculate molar mass using depression in freezing point
10. Important Formula Sheet
- M = n/V
- m = n/kg
- ΔTb = Kb m
- ΔTf = Kf m
- π = CRT
- Raoult’s law
11. Concept Clarity (Very Important)
👉 WHY vapour pressure decreases?
Because solute reduces escaping tendency of solvent.
👉 WHY boiling point increases?
Because more energy needed to vaporize.
👉 WHY freezing point decreases?
Because solute disrupts crystal formation.
👉 WHY osmotic pressure important?
Used in reverse osmosis and biology.
12. Common Mistakes
- Confusing molarity and molality
- Wrong units
- Ignoring van’t Hoff factor
Conclusion
Solutions is a highly important and scoring chapter. It combines theory with numericals and is frequently asked in exams.
👉 Focus on:
- Colligative properties
- Formulas
- Numerical practice