Chapter: Solutions (Class 12, NCERT)

 Worksheet on Henry’s Law and Raoult’s Law

Chapter: Solutions (Class 12, NCERT)

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Q1. Henry’s Law Conceptual Question

Explain Henry’s law and write its mathematical expression. How does the solubility of a gas in a liquid change with:

a) Increase in pressure?

b) Increase in temperature?

Answer:

Henry’s Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the surface of the liquid at a constant temperature.

Effect of Pressure:

As pressure increases, the solubility of the gas in the liquid increases. This is because a higher number of gas molecules are forced into the liquid phase.

Effect of Temperature:

As temperature increases, the solubility of the gas in the liquid decreases. Higher temperatures provide more kinetic energy to gas molecules, making them escape from the liquid.

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Q2. Numerical on Henry’s Law

The Henry’s law constant for CO₂ in water at 25°C is 3.3 × 10⁴ kPa. Calculate the solubility of CO₂ in water at 25°C if the partial pressure of CO₂ over the solution is 2 atm.

(Given: 1 atm = 101.3 kPa)

Solution:

Thus, the solubility of CO₂ in water at 25°C is 0.00614 mol/L.

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Q3. Raoult’s Law Conceptual Question

State Raoult’s law and derive its mathematical expression for a binary liquid solution. How does Raoult’s law explain the concept of ideal and non-ideal solutions?

Answer:

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

Ideal vs. Non-Ideal Solutions:

Ideal solutions obey Raoult’s law at all concentrations. They show no volume change or enthalpy change when mixed (e.g., benzene and toluene).

Non-ideal solutions deviate from Raoult’s law due to stronger or weaker intermolecular forces than in pure components. They show positive or negative deviations (e.g., ethanol and water).

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Q4. Numerical on Raoult’s Law

A solution is prepared by dissolving 10 g of urea (Molar mass = 60 g/mol) in 100 g of water. Calculate the vapor pressure of water in the solution at 25°C.

(Given: Vapor pressure of pure water at 25°C = 23.8 mmHg)

Solution:

Vapour pressure in the solution is 23.1 mmHg.

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Q5. Application-Based Question

Both Henry’s law and Raoult’s law describe the behavior of gases and liquids in solutions. Explain how these laws apply in the following real-life scenarios:

a) Carbonated Soft Drinks

Henry’s law explains why CO₂ dissolves in soft drinks under high pressure. When the bottle is sealed, the high pressure keeps CO₂ dissolved. Upon opening, the pressure decreases, causing CO₂ to escape as bubbles.

b) Deep-Sea Diving

Henry’s law explains nitrogen narcosis. At great depths, divers experience high pressure, leading to more nitrogen dissolving in their blood. If they ascend too quickly, nitrogen comes out as bubbles, causing decompression sickness ("the bends").

c) Boiling of Water at High Altitudes

Raoult’s law helps explain why water boils at lower temperatures at high altitudes. At higher elevations, atmospheric pressure is lower, reducing the boiling point of water because it reaches equilibrium with atmospheric vapor pressure at a lower temperature.

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Conclusion:

This worksheet covered Henry’s Law and Raoult’s Law with conceptual, numerical, and application-based questions. Let me know if you need further explanations!