Osmotic Pressure Calculator

The van't Hoff factor (i) counts how many dissolved particles each formula unit produces. A non-electrolyte like glucose stays as one particle per molecule (i = 1), while NaCl dissociates into Na+ and Cl- (i = 2 in the ideal case), doubling the osmotic pressure of an equally molar salt solution compared to an equally molar sugar solution.

Not in the formula itself: Molarity, Temperature, and the van't Hoff Factor all enter the pressure equation multiplicatively, so a given percentage change in any one produces the same percentage change in pressure. In practice, Molarity tends to swing results the most because its allowed range in this calculator spans six orders of magnitude (0.0001 to 100 M), far wider than the realistic ranges for Temperature or the van't Hoff Factor.

No. The van't Hoff equation assumes dilute, ideal-solution behavior, treating solute particles as non-interacting. At high molarity, real solutions deviate from this ideal prediction because ions and molecules interact with each other, so the true osmotic pressure at very high concentrations will typically be somewhat lower than this calculator reports.

Add 273.15 to a Celsius temperature to get Kelvin -- the calculator's default of 298.15 K corresponds to 25°C (standard room temperature). Osmotic pressure calculations always require absolute temperature because the underlying gas-law relationship is only valid on the Kelvin scale, where zero represents true zero thermal energy.

Osmolarity is the total concentration of dissolved particles, equal to Molarity multiplied by the van't Hoff Factor (i x M). For a non-dissociating solute like glucose, Osmolarity equals Molarity; for an electrolyte like NaCl that splits into two ions, Osmolarity is twice the Molarity, which is why it is the more clinically relevant number for comparing solutions with different solutes.