William Henry made systematic studies of the solubility of a gas in a liquid. He gave a quantitative relationship between the solubility of a gas in a solvent and pressure which is known as Henry’s law. The law states that- the mass of a gas dissolved per unit volume of the solvent at a constant temperature is directly proportional to the pressure of the gas in equilibrium with the solution.

If m is the mass of the gas dissolved in a unit volume of the solvent and p is the pressure of the gas in equilibrium with the solution, then

\[m \propto p\]

\[or,  m = K.p\]

where K is the proportionality constant. The magnitude of K depends on the nature of the gas, the nature of the solvent, the temperature and the units of pressure. Thus, Henry’s law may also be stated as: the solubility of a gas in a liquid at a particular temperature is directly proportional to the pressure of the gas in equilibrium with the solution.

Which one of the following statements regarding Henry's law is not correct?

1. The value of \(K_H\) increases with the function of the nature of the gas
2. Higher the value of \(K_H\) at a given pressure, higher is the solubility of the gas in the liquids.
3. The partial pressure of gas in vapour phase is proportional to the mole fraction of the gas in the solution.
4. Different gases have different \(K_H\) values at the same temperature.

2

The correct statements are 1, 3, and 4. Statement 2 is not correct.

• Statement 1: The value of \(K_H\) increases with the function of the nature of the gas.

This is correct because the \(K_H\) value depends on the intermolecular forces between the gas molecules and the solvent molecules. Different gases have different intermolecular forces, so they will have different \(K_H\) values.

• Statement 2: Higher the value of \(K_H\) at a given pressure, higher is the solubility of the gas in the liquids.

This is not correct. The solubility of a gas in a liquid is directly proportional to the (K_H) value, but not the other way around. So, a higher \(K_H\) value means that the gas is more soluble, but a more soluble gas does not necessarily have a higher \(K_H\) value.

• Statement 3: The partial pressure of gas in vapour phase is proportional to the mole fraction of the gas in the solution.

This is correct. Henry's law states that the partial pressure of a gas in a solution is proportional to the mole fraction of the gas in the solution. This means that if the mole fraction of a gas in a solution increases, the partial pressure of the gas in the vapour phase will also increase.

• Statement 4: Different gases have different \(K_H\) values at the same temperature.

This is correct. As mentioned earlier, the \(K_H\) value depends on the intermolecular forces between the gas molecules and the solvent molecules. Different gases have different intermolecular forces, so they will have different \(K_H\) values at the same temperature.

Therefore, the only incorrect statement is statement 2. The correct answer is 2.