LEVEL 1 WORKSHEET CHAPTER SOLUTION

 Class 12 Chemistry Chapter – Solutions, based on NCERT and CBSE Board Exam patterns, along with answers:

---

1. Define mole fraction. How is it calculated?

Answer:
Mole fraction of a component in a solution is the ratio of number of moles of that component to the total number of moles of all components present in the solution.

$$\text{Mole fraction of A, } x_A = \frac{n_A}{n_A + n_B}$$

---

2. State Henry’s Law. Write its two applications.

Answer:
Henry’s Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas over the liquid.

$$C = k_H \cdot P$$

Where
$C$ = concentration of gas,
$P$ = partial pressure, $k_H$ = Henry's constant.

Applications:

1. In carbonated beverages (soda), CO₂ is dissolved under high pressure.

2. Scuba divers experience bends due to release of N₂ gas dissolved under high pressure.

---

3. What are ideal and non-ideal solutions? Give one example of each.

Answer:

• Ideal Solution: A solution that obeys Raoult’s law at all concentrations.
  Example: Benzene + Toluene

• Non-Ideal Solution: A solution that does not obey Raoult’s law.
  Example: Ethanol + Acetone

---

4. What is Raoult’s Law? Write its mathematical expression for a binary solution.

Answer:
Raoult’s Law states that the partial vapor pressure of a component in a solution is directly proportional to its mole fraction.

For component A and B:

$$P_A = x_A P_A^0 \quad \text{and} \quad P_B = x_B P_B^0$$

Total pressure:

$$P_{total} = P_A + P_B = x_A P_A^0 + x_B P_B^0$$

---

5. What is an azeotrope? Name two types with one example each.

Answer:
Azeotropes are binary mixtures that boil at constant temperature and cannot be separated by fractional distillation.

Types:

1. Minimum boiling azeotrope – Ethanol + Water

2. Maximum boiling azeotrope – HCl + Water

---

6. Define colligative properties. Name four such properties.

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

Examples:

1. Relative lowering of vapor pressure

2. Elevation of boiling point

3. Depression of freezing point

4. Osmotic pressure

---

7. Derive the formula for depression in freezing point.

Answer:

$$\Delta T_f = K_f \cdot m$$

Where:

• $\Delta T_f$ = depression in freezing point

• $K_f$ = cryoscopic constant

• $m$ = molality of solution

---

8. Define van’t Hoff factor (i). What is its significance?

Answer:
Van’t Hoff factor (i) is the ratio of the actual number of particles in solution after dissociation/association to the number of formula units dissolved.

$$i = \frac{\text{Observed colligative property}}{\text{Calculated colligative property (assuming no dissociation/association)}}$$

Significance: It accounts for ionisation/dissociation (i > 1) and association (i < 1).

---

9. Calculate the osmotic pressure of a solution prepared by dissolving 0.5 mol of glucose in 1 L of water at 27°C. (R = 0.0821 L·atm/mol·K)

Answer:

$$\pi = C R T = (0.5)(0.0821)(300) = 12.315 \, \text{atm}$$

---

10. A solution of urea (mol. mass = 60 g/mol) is prepared by dissolving 18 g of urea in 100 g of water. Calculate the lowering in vapor pressure if vapor pressure of pure water at 298 K is 23.8 mmHg.

Answer:

$$\text{Moles of urea} = \frac{18}{60} = 0.3$$ $$\text{Moles of water} = \frac{100}{18} \approx 5.56$$ $$x_{\text{urea}} = \frac{0.3}{0.3 + 5.56} \approx 0.051$$ $$\text{Lowering in vapor pressure} = P^0 \cdot x_{\text{urea}} = 23.8 \cdot 0.051 \approx 1.21 \, \text{mmHg}$$