How to Calculate Osmotic Pressure
What is Osmotic Pressure?
Osmotic pressure is the pressure needed to prevent osmosis — the flow of solvent across a semipermeable membrane from dilute to concentrated solution. π = MRT, where M is molarity, R is the gas constant, and T is temperature in Kelvin.
Step-by-Step Guide
- 1π = M × R × T
- 2R = 0.08206 L·atm/mol·K
- 3M = molar concentration of solute
- 4T = temperature in Kelvin
- 5For electrolytes: multiply by van't Hoff factor i
Worked Examples
Input
0.1M NaCl solution at 25°C (298K) · i=2
Result
π = 0.2×0.08206×298 = 4.89 atm
NaCl dissociates completely → i=2
Ready to calculate? Try the free Osmotic Pressure Calculator
Try it yourself →