Class 12 Chemistry Chapter 2 Solutions Notes

The chapter Solutions in CBSE Class 12 Chemistry plays an important role in physical chemistry and introduces concepts such as types of solutions, concentration methods, Raoult’s law, colligative properties, and Henry’s law. It builds foundational knowledge used in chemical thermodynamics, equilibrium, and even biology.

These Class 12 Chemistry Solutions Notes are created for quick understanding and thorough revision before exams. They are fully aligned with the latest CBSE Class 12 chemistry syllabus and provide concept clarity, formulae, numerical approaches, and solved examples.

Solutions Class 12 Notes Material PDF Download

This study material for Class 12 explains the basics of Solutions in an easy-to-understand way. Download the PDF to learn key concepts and prepare well for your exams.

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Important Notes from Solutions Class 12

Below given are perfect notes for last minute revision purposes:

1. Types of Solutions

Binary Solutions: Solutions containing two components.

• Solute: Present in lesser amount
• Solvent: Present in larger amount

Classification by phase:

2. Concentration Terms

• Mass % = (mass of solute / mass of solution) × 100
• Volume % = (volume of solute / volume of solution) × 100
• Molarity (M) = moles of solute / volume of solution (L)
• Molality (m) = moles of solute / mass of solvent (kg)
• Mole Fraction (χ) = moles of a component / total moles of all components

Molality is temperature-independent, while molarity is temperature-dependent.

3. Solubility

• Solid in Liquid: Increases with temperature.
• Gas in Liquid: Decreases with temperature, increases with pressure.

Henry’s Law:
The solubility of a gas in a liquid is directly proportional to the pressure of the gas over the solution. p = kH × x; where:

• p = partial pressure of gas
• x = mole fraction of gas
• kH = Henry’s law constant

4. Vapour Pressure of Liquid Solutions

(i) Raoult’s Law

For a solution of two volatile liquids:
PA = P°A × xA,
PB = P°B × xB,
Ptotal = PA + PB

• Ideal Solutions follow Raoult’s Law throughout.
• Non-ideal Solutions deviate (positive/negative) and may form azeotropes.

5. Colligative Properties

Depends on the number of solute particles, not their nature.

‍

Where:

• Kb, Kf = Molal elevation/depression constants
• m = Molality
• R = Gas constant
• T = Temperature in Kelvin

6. Abnormal Molar Mass & Van’t Hoff Factor

Some solutes dissociate or associate in solution, affecting the calculated molar mass.

Van’t Hoff Factor (i) = Observed colligative property / Calculated colligative property

• For association, i < 1 (e.g., acetic acid in benzene)
• For dissociation, i > 1 (e.g., NaCl in water)

Corrected formulas:

• ΔTb = i × Kb × m
• ΔTf = i × Kf × m
• π = iCRT

Important Questions from Chapter: Solutions Class 12

1. Very Short Answer Questions (1 Mark Each)

Q: Define mole fraction.
Ans: Mole fraction is the ratio of moles of one component to the total moles of all components in the solution.

Q: Why is osmotic pressure considered a colligative property?
Ans: Osmotic pressure depends only on the number of solute particles, not their nature, hence it's a colligative property.

Q: What happens to solubility of a gas with rise in temperature?

Ans: Solubility of a gas decreases with rise in temperature.

2. Short Answer Questions (2–3 Marks Each)

Q: State Raoult’s law for a binary solution.
Ans: Raoult’s Law: For a binary solution, the partial vapor pressure of each component is directly proportional to its mole fraction in the solution.

Q: What is an azeotrope? Give one example.
Ans: Azeotrope: A constant-boiling mixture that distills without changing composition. Example: Ethanol–water (95.6% ethanol).

Q: Differentiate between molarity and molality.

Ans: Molarity is moles of solute per liter of solution; Molality is moles of solute per kg of solvent.

3. Long Answer Questions (4–5 Marks Each)

Q: Derive the expression for depression in freezing point.

Ans: Depression in Freezing Point (ΔTf):

When a non-volatile solute is added, the freezing point of the solution lowers:

ΔT_f = K_f ⋅m

where ΔT_f​ is the depression in freezing point, K_f is the cryoscopic constant, and mmm is the molality of the solution.

Q: Explain ideal and non-ideal solutions with examples and graphs.

Ans: Ideal and Non-Ideal Solutions:

1. Ideal Solutions obey Raoult’s law at all concentrations and have no enthalpy or volume change on mixing. Example: Benzene and toluene.

2. Non-Ideal Solutions show positive or negative deviations from Raoult’s law with enthalpy/volume changes. Examples:

• Positive deviation: Ethanol + acetone
• Negative deviation: HCl + water
  (Graphs show deviation of vapor pressure from linearity)

Q: A solution contains 5g of a non-volatile solute in 95g of water. Calculate the boiling point elevation if Kb = 0.512 K·kg/mol.

Ans: Given:

Mass of solute = 5 g

Mass of solvent (water) = 95 g = 0.095 kg

Kb ​= 0.512K \ mol

Assume molar mass of solute (M) = M (since not given, leave in terms of M):

Molality (m)  = 5 / M x 0.095

ΔT_b ​= K_b ​⋅ m 

= 0.512 . 5 / M x 0.095

= 2.56 / 0.095M

= 26.95M K 

So, boiling point elevation = 26.95M K

Common Mistakes to Avoid

Let’s just avoid these mistakes given below and excel in our exams:

🚫 Mixing up molarity and molality (especially in numerical units).

🚫 Not converting temperature to Kelvin in colligative property calculations.

🚫 Ignoring Van’t Hoff factor in dissociation/association problems.

🚫 Confusing ideal and non-ideal solutions based on Raoult’s law.

🚫 Incorrect application of Raoult’s law when both components are volatile.

Creative Ways to Make Notes for Solutions Chapter

Let’s have a look at how to turn boring chapters into fun notes to study effectively:

1. Concept Maps: Link concentration terms, laws, and properties with arrows and keywords.
2. Formula Chart: Create a dedicated formula page with units and variable definitions.
3. Comparison Tables: Contrast molarity vs molality, ideal vs non-ideal, etc.
4. Flowcharts: Use for derivations or step-by-step numerical solving.
5. Color-coded Flashcards: For quick revision of laws, constants, and definitions.

How Can Notes Help?

Here are certain ways on how notes could actually be beneficial for you:

• Provide quick conceptual recall before board exams.
• Offer ready-to-use formulas and structured theory for numericals.
• Help identify the type of solution and apply the correct law or formula.
• Strengthen conceptual clarity to avoid confusion during MCQs or case-based questions.
• Serve as a summary guide during last-moment revision or mock tests.

The Solutions chapter in Class 12 Chemistry is packed with fundamental principles that lay the groundwork for higher-level chemistry and competitive exams. Whether it's understanding how solutes behave or mastering colligative properties, clear, organized notes make a big difference.

Use these notes to revise key terms, formulas, and conceptual frameworks, and build confidence for both CBSE board and entrance exams.

Frequently Asked Questions

1. What is a solution in chemistry?

Answer: A solution is a homogeneous mixture composed of two or more substances. The component present in the largest amount is called the solvent, and the substance(s) present in smaller amounts are called solutes. A solution can be liquid, solid, or gas.

2. What is the difference between a solvent and a solute?

Answer: The solvent is the component of the solution that dissolves the solute and is usually present in a larger quantity. The solute is the substance that is dissolved in the solvent and is present in a smaller quantity.

3. What are the different types of solutions?

Answer: Solutions can be classified based on the physical state of the solvent and solute:

• Gas in gas (e.g., air)
• Liquid in gas (e.g., water vapor in air)
• Solid in liquid (e.g., sugar in water)
• Liquid in liquid (e.g., alcohol in water)
• Solid in solid (e.g., alloys like brass)
• Gas in liquid (e.g., carbonated water)

4. What is concentration in a solution?

Answer: Concentration refers to the amount of solute dissolved in a given quantity of solvent or solution. It can be expressed in various ways, such as molarity (M), molality (m), percent by weight, or volume, etc.

5. What is molarity and how is it calculated?

Answer: Molarity (M) is the number of moles of solute present in one liter of solution. It is calculated as:
M = moles of solute / vol of solution (in litres)

6. What is molality and how is it different from molarity?

Answer: Molality (m) is the number of moles of solute dissolved in one kilogram of solvent. Unlike molarity, which depends on the volume of the solution, molality depends on the mass of the solvent and remains unaffected by temperature changes.

7. What is the difference between an unsaturated, saturated, and supersaturated solution?

Answer:

• Unsaturated solution: A solution that can dissolve more solute at a given temperature.
• Saturated solution: A solution that contains the maximum amount of solute that can dissolve at a given temperature.
• Supersaturated solution: A solution that contains more solute than it can theoretically dissolve at a given temperature. This is an unstable condition.

8. What are colligative properties?

Answer: Colligative properties are properties of solutions that depend on the number of solute particles but not their identity. The main colligative properties are:

• Boiling point elevation
• Freezing point depression
• Vapor pressure lowering
• Osmotic pressure

9. What is the effect of temperature on solubility?

Answer: Generally, the solubility of most solids in liquids increases with an increase in temperature. For gases, however, solubility usually decreases with an increase in temperature.

10. What is osmosis and osmotic pressure?

Answer: Osmosis is the movement of solvent molecules from a region of lower solute concentration to a region of higher solute concentration through a semipermeable membrane. Osmotic pressure is the pressure required to stop the osmotic flow of solvent, and it is directly proportional to the concentration of the solute particles.