How is osmotic pressure measured and calculated?

Osmotic pressure is measured using an osmometer and calculated using the formula π = nRT/V.

Osmotic pressure is a colligative property, meaning it depends on the number of solute particles in a solution, not their identity. It's the pressure required to prevent osmosis, the movement of solvent from an area of low solute concentration to an area of high solute concentration.

To measure osmotic pressure, an osmometer is used. This device consists of two compartments separated by a semi-permeable membrane. One compartment contains the solution whose osmotic pressure is to be measured, and the other contains a pure solvent. The solvent naturally moves across the membrane to the solution side, creating a pressure difference. This pressure difference is measured and is equal to the osmotic pressure of the solution.

The osmotic pressure (π) can be calculated using the formula π = nRT/V, where n is the number of moles of solute, R is the ideal gas constant, T is the temperature in Kelvin, and V is the volume of the solution in litres. This formula is derived from the ideal gas law, which states that the pressure of a gas is directly proportional to its temperature and number of moles, and inversely proportional to its volume.

In practice, the osmotic pressure is often used to determine the molar mass of a solute. By measuring the osmotic pressure at a known temperature and volume, and knowing the ideal gas constant, the number of moles of solute can be calculated. From this, the molar mass can be determined.

Remember, osmotic pressure is a vital concept in many biological processes, including the functioning of cells. It's also used in various industrial processes, such as reverse osmosis for water purification.