Solutions – Class 12 Chemistry Notes

 🧪 Chapter 2: Solutions – Class 12 Chemistry Notes

Label: Chemistry, Class 12, Solutions

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🔹 Introduction

A solution is a homogeneous mixture of two or more substances.

The component present in larger quantity is called solvent, and the one in smaller quantity is called solute.

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🧫 Types of Solutions (Based on Physical State)

Type Solute Solvent Example

Solid in liquid Sugar Water Sugar solution

Gas in liquid CO₂ Water Soda water

Liquid in liquid Alcohol Water Alcohol in water

Solid in solid Copper Gold Alloy (Gold coin)

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📏 Concentration of Solutions

1. Mass Percentage (w/w):

= (Mass of solute / Mass of solution) × 100

2. Volume Percentage (v/v):

= (Volume of solute / Volume of solution) × 100

3. Molarity (M):

= (Moles of solute / Volume of solution in L)

4. Molality (m):

= (Moles of solute / Mass of solvent in kg)

5. Mole Fraction (χ):

= (Moles of component / Total moles of all components)

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⚠️ Solubility

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

✔ Factors affecting solubility:

Nature of solute and solvent

Temperature

Pressure (for gases)

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⬇️ Henry’s Law (for gases in liquids)

p = KH × x

Where:

p = Partial pressure of gas

KH = Henry’s law constant

x = Mole fraction of gas in liquid

> Higher pressure → more solubility of gas

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⬆️ Raoult’s Law

For a solution of volatile liquids:

Pₐ = xₐ × Pₐ°

Where:

Pₐ = Partial vapour pressure

xₐ = Mole fraction

Pₐ° = Vapour pressure of pure component

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📉 Ideal and Non-Ideal Solutions

Type Obeys Raoult's Law? Heat Change Volume Change

Ideal Yes No No

Non-Ideal No Yes Yes

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🔁 Colligative Properties

(Properties depending only on number of solute particles)

1. Relative lowering of vapour pressure

2. Elevation of boiling point

ΔTb = Kb × m

3. Depression of freezing point

ΔTf = Kf × m

4. Osmotic pressure

π = CRT

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🔍 Abnormal Molar Mass

Due to association or dissociation of solute particles.

Van’t Hoff Factor (i):

i = Normal molar mass / Observed molar mass

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📌 Important Terms

Azeotrope – A constant boiling mixture

Hypertonic solution – Higher concentration than cell

Hypotonic solution – Lower concentration

Isotonic – Equal concentration

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📝 Quick Revision Table

Concept Formula

Molarity (M) n / V (L)

Molality (m) n / mass of solvent (kg)

Mole Fraction (χ) n₁ / (n₁ + n₂)

Raoult’s Law Pₐ = xₐ × Pₐ°

Elevation in B.P. ΔTb = Kb × m

Depression in F.P. ΔTf = Kf × m

Osmotic Pressure π = C × R × T

Van’t Hoff Factor i = Normal M / Observed M

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✅ Summary

Solution: Homogeneous mixture

Concentration can be measured in many ways

Raoult’s Law and Henry’s Law explain vapour pressure & gas solubility

Four colligative properties de

pend on number of solute particles

Molar mass may appear abnormal due to association/dissociation

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✍️ Written by Shahid – Founder of Shahid Notes

📚 Visit: https://shahidnotes12.blogspot.com