Question

State Henry's law and its important applications.

Hint:

Henry's law: the partial pressure of a gas is proportional to its mole fraction in solution, \(p = K_H x\). Think of soda bottles, scuba diving and high-altitude anoxia.

Answer 1

Step 1: Statement of Henry's law. At a constant temperature the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. In other words, the partial pressure of the gas \((p)\) in the vapour phase is proportional to its mole fraction \((x)\) in the solution.
Step 2: Mathematical form.
\[p = K_H\, x\]
where \(K_H\) is the Henry's law constant. A higher value of \(K_H\) means lower solubility of the gas.
Step 3: Applications.
• Soft drinks and soda water: to dissolve more CO₂, the bottles are sealed under high pressure of carbon dioxide.
• Deep-sea (scuba) diving: at depth the high pressure increases the solubility of nitrogen in blood; while coming up it bubbles out and causes 'bends', so divers use air diluted with helium, which is less soluble.
• High altitudes: the partial pressure of oxygen is low, so less oxygen dissolves in a climber's blood, causing weakness and poor thinking (anoxia).