Enter the number of ions produced from dissociation, osmotic coefficient, concentration, and temperature into the calculator to determine the osmotic pressure.

Osmotic Pressure Formula

The following equation is used to calculate and osmotic pressure.

O = n * ce * C * R * T

  • Where O is the osmotic pressure (pascals)
  • C is the concentration mol/L
  • n is the number of ions produces during dissociation
  • ce is the osmotic coefficient
  • R is the Universal gas constant (8.314 J / K*mol)
  • T is the temperature in K

Osmotic Pressure Definition

Osmotic pressure is defined as the pressure needed to stop the flow of a solution through a membrane.

Osmotic Pressure Example Problem

The following is an example problem of how to calculate an osmotic pressure.

First, we must determine the concentration of the solution. Through analysis, we determine that this value is 10 mol/L of NaCl.

Next, we need to determine the number of ions produced by dissociation. Using a lookup table we see that NaCl has a value of 52.

Next, we determine the osmotic coefficient through experimental data and find it to be .93.

Next, determine the temperature during the osmotic process. It’s determined that this value is 100K.

Finally, using the information we gathered and the equation presented above, we determine the osmotic pressure to be 402,065 Pa.


What is osmotic pressure?

Osmotic pressure is the pressure required to prevent the flow of a solution through a membrane. It’s often described as the “minimum” pressure to stop the process of osmosis from occurring.

What is the osmotic coefficient?

The osmotic coefficient is a value derived from the type of solution that’s attempting to go through osmosis. For NaCl it is equal to .93 and for KCl it is equal to .92.

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osmotic pressure formula