Osmotic Pressure Calculator
Compute the osmotic pressure of a solution from its molarity, temperature and van’t Hoff factor using the van’t Hoff equation.
How it works
Π = i × M × R × T · R = 0.08206 L·atm/(mol·K) · T in kelvin
Osmotic pressure is the pressure needed to stop solvent flowing across a semipermeable membrane into a solution. The van’t Hoff equation Π = iMRT mirrors the ideal gas law, with molarity playing the role of concentration and the van’t Hoff factor accounting for solutes that dissociate. It is a colligative property, so it scales with the number of dissolved particles.
Worked example
A 0.10 mol/L solution of a non-electrolyte at 25 °C (298.15 K): Π = 1 × 0.10 × 0.08206 × 298.15 = 2.446 atm, which is about 248 kPa.
Sources: Osmotic pressure — Wikipedia
Frequently asked questions
Why does the equation look like the ideal gas law?
Because dilute solutes behave much like an ideal gas dispersed in the solvent. Π = iMRT is the solution-phase analogue of P = nRT/V, with molarity replacing n/V.
What temperature units does R require?
Kelvin. Using R = 0.08206 L·atm/(mol·K) means T must be the Celsius temperature plus 273.15; the tool converts this for you.
Why include the van’t Hoff factor?
Ionic solutes dissociate, so one mole of NaCl produces about two moles of particles (i ≈ 2), roughly doubling the osmotic pressure compared with a non-electrolyte at the same molarity.
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This calculator is for educational purposes. Double-check important results before acting on them.