Worksheet Based on Solutions

10 questions from the Chapter: Solutions (Class 12 Chemistry, NCERT-based), selected based on their relevance and frequency in CBSE Board Exams:

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1. Define molality and write its unit. How does molality differ from molarity with respect to temperature dependence?

2. State and explain Raoult’s law for a solution containing a non-volatile solute.

3. Differentiate between ideal and non-ideal solutions with suitable examples.

4. What is azeotrope? Explain minimum boiling and maximum boiling azeotropes with examples.

5. State Henry’s law. What is the effect of temperature on Henry’s law constant?

6. Define the term colligative properties. Name four colligative properties and mention which one is most used to determine molar mass.

7. Derive the expression for relative lowering of vapour pressure in terms of mole fraction of solute.

8. What is van’t Hoff factor? How does it account for the abnormal molar mass of solutes?

9. Calculate the osmotic pressure of a solution and derive the relation between osmotic pressure and molar mass.

10. A solution prepared by dissolving a non-volatile solute in a solvent has a boiling point higher than that of the pure solvent. Explain the phenomenon.

Numericals for practice from the chapter Solutions Class 12 Chemistry

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Here are the 10 very important questions from the chapter Solutions (Class 12 Chemistry) along with their answers, based on CBSE board exam patterns:

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1. Define molality and write its unit. How does molality differ from molarity with respect to temperature dependence?

Answer:
Molality (m) is defined as the number of moles of solute per kilogram of solvent.
Unit: mol/kg

Difference:
Molality is independent of temperature because it is based on mass, whereas molarity depends on temperature as it is based on volume, which changes with temperature.

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2. State and explain Raoult’s law for a solution containing a non-volatile solute.

Answer:
Raoult’s law states that the relative lowering of vapour pressure of a dilute solution is equal to the mole fraction of the solute.

For a non-volatile solute:

$$P_{\text{solution}} = P^0_{\text{solvent}} \times X_{\text{solvent}}$$

Where $P^0_{\text{solvent}}$ is the vapour pressure of the pure solvent, and $X_{\text{solvent}}$ is its mole fraction.

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3. Differentiate between ideal and non-ideal solutions with suitable examples.

Answer:

Property	Ideal Solution	Non-Ideal Solution
Enthalpy change	$\Delta H_{\text{mix}} = 0$	$\Delta H_{\text{mix}} \neq 0$
Volume change	$\Delta V_{\text{mix}} = 0$	$\Delta V_{\text{mix}} \neq 0$
Example	Benzene + Toluene	Acetone + Chloroform

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4. What is azeotrope? Explain minimum boiling and maximum boiling azeotropes with examples.

Answer:
An azeotrope is a mixture of two or more liquids that boils at a constant temperature and behaves like a pure substance.

• Minimum boiling azeotrope: Shows positive deviation, e.g., Ethanol + Water.

• Maximum boiling azeotrope: Shows negative deviation, e.g., HCl + Water.

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5. State Henry’s law. What is the effect of temperature on Henry’s law constant?

Answer:
Henry’s law: The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

$$C = k_H \cdot P$$

Where $C$ is the concentration, $k_H$ is Henry’s constant, and $P$ is pressure.

Effect of temperature:
As temperature increases, Henry’s law constant ($k_H$) increases, hence the solubility of the gas decreases.

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6. Define the term colligative properties. Name four colligative properties and mention which one is most used to determine molar mass.

Answer:
Colligative properties are those properties of solutions that depend on the number of solute particles but not on their nature.

Examples:

1. Relative lowering of vapour pressure

2. Elevation in boiling point

3. Depression in freezing point

4. Osmotic pressure

Most commonly used for molar mass determination: Osmotic pressure.

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7. Derive the expression for relative lowering of vapour pressure in terms of mole fraction of solute.

Answer:
For a solution with non-volatile solute:

$$\frac{P^0 - P}{P^0} = X_{\text{solute}}$$

Where:

• $P^0$ = vapour pressure of pure solvent

• $P$ = vapour pressure of solution

• ( X_{\text{solute}} _