NCERT Solutions Class 12 Chemistry Chapter 2 – Solutions

NCERT Solutions for Class 12 Chemistry Chapter 2: Solutions

This chapter covers types of solutions, concentration units, Raoult’s law, colligative properties, and abnormal molar masses. It is important for both boards (8-10 marks) and competitive exams.

Exercise Questions and Solutions

Q1. Calculate the mass percentage of benzene (C₆H₆) and carbon tetrachloride (CCl₄) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.

Solution:

Total mass = 22 + 122 = 144 g

Mass % of benzene = (22/144) × 100 = 15.28%

Mass % of CCl₄ = (122/144) × 100 = 84.72%

Q2. Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.

Solution:

Assume 100 g of solution: 30 g benzene + 70 g CCl₄

Moles of benzene = 30/78 = 0.385 mol

Moles of CCl₄ = 70/154 = 0.455 mol

Mole fraction of benzene = 0.385/(0.385 + 0.455) = 0.458

Q3. Calculate the molarity of a solution containing 5 g of NaOH in 450 mL solution.

Solution:

Moles of NaOH = 5/40 = 0.125 mol

Volume = 450 mL = 0.45 L

Molarity = 0.125/0.45 = 0.278 M

Q4. The boiling point of benzene is 353.23 K. When 1.80 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11 K. Calculate the molar mass of the solute. (Kb for benzene = 2.53 K kg mol⁻¹)

Solution:

ΔTb = 354.11 – 353.23 = 0.88 K

ΔTb = Kb × m

0.88 = 2.53 × (1.80/M × 1000/90)

0.88 = 2.53 × 20/M

M = 2.53 × 20/0.88 = 57.5 g/mol

Important Formulas

Key Takeaways

• Solutions are homogeneous mixtures of two or more components
• Colligative properties depend on number of particles, not nature
• Raoult’s law: partial vapor pressure ∝ mole fraction
• Ideal solutions obey Raoult’s law; non-ideal show deviations
• For electrolytes, use Van’t Hoff factor (i) in formulas
• Osmotic pressure is used to determine molar mass of polymers