The Solutions chapter in Class 12 Chemistry is one of the most important and scoring chapters for CBSE Board Exams and competitive exams like NEET, JEE (Main), CUET, and state-level entrance tests. This chapter mainly deals with types of solutions, concentration of solutions, solubility, vapor pressure, Raoult’s law, colligative properties, and abnormal molar mass.
Many numerical questions are asked from this chapter every year. If you understand the concepts clearly and practice enough problems, you can easily score full marks. In this blog, you will find complete Class 12 Chemistry Solutions Notes PDF explained in simple language, along with important formulas and exam-focused points.
Class 12 Chemistry Solutions Notes PDF| Important Questions & Numericals
What is a Solution?
A solution is a homogeneous mixture of two or more substances.
- The substance present in larger amount is called solvent
- The substance present in smaller amount is called solute
Examples
- Sugar in water → Sugar (solute), Water (solvent)
- Salt in water → Salt (solute), Water (solvent)
- Air → Mixture of gases (solution of gases)
Types of Solutions
Solutions are classified based on the physical state of solute and solvent.
1. Solid in Liquid Solution
Example: Salt in water, Sugar in water
2. Liquid in Liquid Solution
Example: Alcohol in water
3. Gas in Liquid Solution
Example: Carbon dioxide dissolved in soft drinks
4. Solid in Solid Solution
Example: Alloys like brass, bronze
Concentration of Solutions
The concentration of a solution tells us how much solute is present in a given amount of solvent or solution.
1. Mass Percentage (w/w)
\text{Mass %} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100
2. Volume Percentage (v/v)
\text{Volume %} = \frac{\text{Volume of solute}}{\text{Volume of solution}} \times 100
3. Mass by Volume Percentage (w/v)
\text{Mass by Volume %} = \frac{\text{Mass of solute}}{\text{Volume of solution}} \times 100
4. Mole Fraction (X)
X_A = \frac{\text{Moles of A}}{\text{Total moles of all components}}
- Mole fraction has no unit
- The sum of mole fractions is always 1
5. Molarity (M)
\text{Molarity} = \frac{\text{Moles of solute}}{\text{Volume of solution in litre}}
⚠️ Temperature dependent (volume changes with temperature)
6. Molality (m)
\text{Molality} = \frac{\text{Moles of solute}}{\text{Mass of solvent in kg}}
✔️ Temperature independent
✔️ Most useful in colligative properties
Solubility
Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a particular temperature.
Effect of Temperature
- Solubility of solids in liquids generally increases with temperature
- The solubility of gases in liquids decreases with an increase in temperature
Vapour Pressure of Liquid Solutions
- The vapour pressure of a solution is less than that of the pure solvent
- The addition of a non-volatile solute lowers the vapour pressure
Raoult’s Law
Statement
The partial vapor pressure of a volatile component in a solution is equal to the vapor pressure of the pure component multiplied by its mole fraction.
P_A = X_A P_A^0
Where:
- = Partial vapour pressure
- = Mole fraction
- = Vapour pressure of pure component
Ideal and Non-Ideal Solutions
Ideal Solutions
- Obey Raoult’s law at all concentrations
- No heat absorbed or evolved
- Volume change is zero
Example: Benzene + Toluene
Non-Ideal Solutions
- Do not obey Raoult’s law
- Show positive or negative deviation
Colligative Properties
Colligative properties depend on the number of solute particles, not their nature.
Types of Colligative Properties
- Relative lowering of vapour pressure
- Elevation of boiling point
- Depression of freezing point
- Osmotic pressure
Elevation of Boiling Point
\Delta T_b = K_b m
Where:
- = Molal elevation constant
- = Molality
Depression of Freezing Point
\Delta T_f = K_f m
Where:
- = Molal depression constant
Osmosis and Osmotic Pressure
Osmosis is the flow of solvent from a dilute solution to a concentrated solution through a semipermeable membrane.
\pi = CRT
Where:
- = Osmotic pressure
- C = Molar concentration
- R = Gas constant
- T = Temperature in Kelvin
Abnormal Molar Mass
Abnormal molar mass occurs due to:
- Association of molecules (e.g., acetic acid)
- Dissociation of molecules (e.g., electrolytes)
van’t Hoff Factor (i)
i = \frac{\text{Observed colligative property}}{\text{Calculated colligative property}}
Important Exam Tips
✔ Focus on numerical problems
✔ Learn formulas by heart
✔ Molality is preferred in colligative properties
✔ Raoult’s law is very important for 1–2 mark questions
Conclusion—Class 12 Chemistry Solutions Notes PDF
The Class 12 Chemistry Solutions Chapter Notes PDF is concept-based and highly scoring if prepared properly. Understanding concentration terms, Raoult’s law, and colligative properties is the key to success in exams. These complete notes will help you revise the chapter quickly and perform well in your board and competitive exams.
Class 12 Chemistry Solutions – Important Questions
Very Short Answer Questions (1 Mark)
- What is a solution?
- Define solute and solvent.
- What is mole fraction?
- Write the formula of molarity.
- Which concentration term is temperature independent?
- What happens to the vapor pressure when a non-volatile solute is added?
- Name any one colligative property.
- Define osmosis.
- What isn’t the Hoff factor?
- Which solution obeys Raoult’s law at all concentrations?
Short Answer Questions (2–3 Marks)
- Define mass percentage and write its formula.
- Explain molality. Why is it preferred over molarity in colligative properties?
- State Raoult’s law for an ideal solution.
- What are ideal solutions? Give one example.
- What is depression in freezing point? Write its mathematical expression.
- Define the elevation of the boiling point.
- Explain abnormal molar mass with one reason.
- What is osmotic pressure? Write its formula.
- Differentiate between molarity and molality (any two points).
- What is the effect of temperature on the solubility of gases in liquids?
Numerical Problems (Very Important)
- Calculate the molarity of a solution containing 5 g NaOH dissolved in 250 mL of water.
- Find the molality of a solution prepared by dissolving 10 g of of urea (molar mass = 60 g/mol) in 500 g of water.
- Calculate the mole fraction of ethanol in a solution containing 2 moles of ethanol and 3 moles of water.
- Determine the elevation in boiling point when 1 mol of glucose is dissolved in 1 kg of water.
- Calculate the depression in freezing point for a solution of 0.2 m NaCl in water.
Long Answer Questions (4–5 Marks)
- Explain Raoult’s law with a neat diagram and mathematical expression.
- What are colligative properties? Explain any two in detail.
- Derive the expression for depression in freezing point.
- Explain osmotic pressure and its applications.
- What isn’t the Hoff factor? Explain its role in the association and dissociation of solute particles.
Case Study / Assertion-Reason Type Questions
- A solution shows a lower vapor pressure than the pure solvent.
- (a) Name the property responsible for this behavior.
- (b) Write the relation for the lowering of vapor pressure.
- Assertion (A): Molality is preferred over molarity in colligative properties.
Reason (R): Molality does not depend on temperature.
⭐ Exam-Focused Tip
📌 Numericals from:
- Molarity & Molality
- Elevation of boiling point
- Depression of freezing point
- Osmotic pressure