Henry’s Law and Its Applications Answers

 

Concept-Based Questions

1. State Henry’s Law. How does it explain the increase in the solubility of CO₂ in soda water when the bottle is sealed under high pressure?

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. Mathematically,

  $$C = k_H P$$

  where:

  • C = concentration (solubility) of the gas,
  • k_H = Henry’s Law constant,
  • P = partial pressure of the gas above the liquid.

• Application in Soda Water:

  • In soft drink bottles, CO₂ is dissolved under high pressure to increase its solubility.
  • When the bottle is opened, the pressure above the liquid decreases, causing CO₂ to escape in the form of bubbles (fizz).

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2. How does Henry’s Law help in understanding the problems faced by scuba divers? Explain the condition called "bends."

Answer:

• Henry’s Law states that gas solubility increases with pressure.
• When scuba divers go deep underwater, the high pressure increases the solubility of gases (especially nitrogen) in their blood.
• When they ascend too quickly, the pressure decreases rapidly, causing dissolved nitrogen to form bubbles in the blood.
• These nitrogen bubbles block capillaries, leading to a painful and potentially fatal condition called "bends" (decompression sickness).

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3. Why do mountaineers suffer from anoxia at high altitudes? Explain with reference to Henry’s Law.

Answer:

• At high altitudes, the partial pressure of oxygen is lower than at sea level.
• According to Henry’s Law, lower pressure reduces the solubility of oxygen in blood, leading to low oxygen levels in tissues.
• This causes anoxia, where climbers feel weak, dizzy, and have difficulty in thinking clearly.

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4. Why do scuba divers use a mixture of helium, nitrogen, and oxygen instead of normal air?

Answer:

• Nitrogen has high solubility in blood at high pressures. When divers ascend rapidly, nitrogen forms bubbles, causing bends.
• To reduce this risk, scuba tanks use a gas mixture containing helium (11.7%), nitrogen (56.2%), and oxygen (32.1%) because:
  • Helium is less soluble in blood than nitrogen, reducing the risk of bends.
  • Helium is non-toxic and lightweight, making breathing easier.

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5. How does temperature affect the solubility of gases in liquids? Explain using Le Chatelier’s Principle.

Answer:

• The dissolution of gases in liquids is an exothermic process (releases heat).
• According to Le Chatelier’s Principle, increasing temperature shifts the equilibrium to reduce heat, decreasing gas solubility.
• This is why:
  • Cold water holds more dissolved oxygen, benefiting aquatic life.
  • Warm water holds less oxygen, which can be harmful to fish.

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Numerical and Application-Based Questions

6. The solubility of oxygen in water at 293 K is 0.048 g/L when the partial pressure of oxygen is 0.21 atm. What will be the solubility of oxygen in water if the partial pressure increases to 0.35 atm?

Solution:

Using Henry’s Law:

$$C_1 = k_H P_1, \quad C_2 = k_H P_2$$

Since $k_H$ is constant, we write:

$$\frac{C_1}{P_1} = \frac{C_2}{P_2}$$

Substituting the values:

$$\frac{0.048}{0.21} = \frac{C_2}{0.35}$$ $$C_2 = \frac{0.048 \times 0.35}{0.21} = 0.08 \text{ g/L}$$

Final Answer: The solubility of oxygen at 0.35 atm is 0.08 g/L.

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7. Why do cold drinks fizz when the bottle is opened? Explain using Henry’s Law.

Answer:

• In a sealed bottle, CO₂ is dissolved under high pressure.
• When the bottle is opened, the pressure above the liquid suddenly decreases, reducing CO₂ solubility.
• The excess CO₂ escapes as bubbles, causing the fizzing effect.

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8. Why is it dangerous to heat carbonated drinks in sealed bottles?

Answer:

• Heating increases temperature, which decreases CO₂ solubility in the liquid.
• Since the bottle is sealed, the released CO₂ increases internal pressure, which may cause the bottle to burst.

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9. How does an increase in temperature affect aquatic life in rivers and lakes with respect to gas solubility?

Answer:

• Higher temperatures decrease oxygen solubility in water.
• This leads to lower oxygen levels, making it difficult for aquatic animals to survive.
• This phenomenon is a major concern in polluted water bodies where thermal pollution from industries raises water temperature.

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10. Why do deep-sea fishes die when brought rapidly to the surface of the ocean? Explain in terms of gas solubility.

Answer:

• Deep-sea fishes live under high pressure, which increases gas solubility in their blood.
• When brought to the surface too quickly, the pressure decreases rapidly, causing dissolved gases to form bubbles inside their bodies.
• This can lead to organ damage and even death, similar to bends in divers.

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Final Thoughts

These questions and solutions cover all key concepts, real-life applications, and numerical problems related to Henry’s Law and gas solubility, making them important for CBSE board exams