What is osmotic pressure?

Question

What is osmotic pressure? I know that it is pressure required to prevent osmosis. But then what does it mean by high osmotic pressure? Does it mean there is more solute on one side, therefore greater concentration gradient ??

what would be some of the properties of solutions which contribute to their osmotic pressure?

Answer 1

Osmotic Pressure = i x M x R x T

i = van't Hoff factor, M = molarity; R = ideal gas constant; T = kelvin temperature.

A higher osmotic pressure is produced when there are more particles in solution (i factor), a higher concentration of solute (M), and a higher temperature.

1 M NaCl has a higher osmotic pressure than 1 M sucrose because NaCl ionizes (i = 2) whereas sucrose doesn't (i = 1).

Another example, 1 M Na3PO4 where i = 4 has a higher osmotic pressure than 1 M Ca(NO3)2 where i = 3.

A higher osmotic pressure means that there is a greater difference in solute concentration on the two sides of the membrane. The solvent, usually water, will move through the membrane toward the side that has more solute particles.

Answer 2

picture a container with a semi-permeable membrane splitting the container in half.  one half has a solution containing high solvent (water in most cases) and low solute (salts like Na+ and Cl-) and the other half has a solution containing low solvent and hight solute.  Because you have a semi-permeable member, only water can travel through the membrane (water being a smaller molecule than salt particles can cross through). the half of the container that has the most water/high solvent will want to cross the membrane and occupy the space in the half that has a lower water/solvent concentration.

the greater the difference in solvent concentrations between the two halves of the container, the greater the water/solvent wants to move to the container with the lower water/solvent concentration, the greater the osmotic pressure needed to prevent this from happening.

the larger the difference it is between one half and the other in terms of solute, the large the osmotic gradient.