Which of the following law is used for calculating osmotic pressure?
**Core Concept**
The osmotic pressure of a solution is a measure of the pressure required to prevent the flow of water into the solution through a semipermeable membrane. It is a colligative property, meaning it depends on the number of solute particles in the solution rather than their identity.
**Why the Correct Answer is Right**
The correct answer is the van 't Hoff factor equation, which is used to calculate the osmotic pressure (π) of a solution. The equation is given by: π = (n * R * T) / V, where n is the number of moles of solute, R is the gas constant, T is the temperature in Kelvin, and V is the volume of the solution. This equation takes into account the number of particles in the solution, which affects the osmotic pressure.
**Why Each Wrong Option is Incorrect**
**Option A:** The ideal gas law (PV = nRT) is used to calculate the pressure of a gas, but it does not account for the number of particles in the solution, making it incorrect for calculating osmotic pressure.
**Option B:** The equation for calculating the freezing point depression (ΔTf) is ΔTf = Kf * m, where Kf is the freezing point depression constant and m is the molality of the solution. This equation is unrelated to osmotic pressure.
**Option C:** The equation for calculating the boiling point elevation (ΔTb) is ΔTb = Kb * m, where Kb is the boiling point elevation constant and m is the molality of the solution. This equation is also unrelated to osmotic pressure.
**Clinical Pearl / High-Yield Fact**
For dilute solutions, the osmotic pressure can be approximated using the equation π = nRT, where n is the number of moles of solute, R is the gas constant, and T is the temperature in Kelvin. This equation is useful for quick calculations, but it assumes that the solution is ideal and the solute particles do not interact with each other.
**Correct Answer:** C. π = (n * R * T) / V.