Question

Osmotic pressure is also a colligative property. What is osmotic pressure? Molarity units are used in the equation to calculate osmotic pressure. When does the molarity of a solution approximately equal the molality of the solution?

Short answer

The minimum external pressure that is exerted on the solution to cease the process of osmosis is known as osmotic pressure. In the case of pure, the molarity and molality of a solution will be equal.

Step-by-step solution

Step 1:

Osmosis is the phenomenon of the movement of solvent particles from their higher concentration to their lower concentration through a semipermeable membrane or we can say the movement of solvent particles from a region of higher concentration to a region of lower concentration.

The semipermeable membrane allows only solvent particles to move from one region to another.

When external pressure is applied to the solution, it disturbs the flow of solvent through the semipermeable membrane, and the process of osmosis stops.

Thus, the minimum amount of external pressure that is required to cease the flow of solvent is known as osmotic pressure.

Step 2:

The relation of osmotic pressure is given as: $\pi \text{=MRT}$

The molarity present in the osmotic pressure deals with the volume whereas molality deals with the mass of the solvent.

The ratio of mass and volume gives the density of a substance. Water has a density which means the value of mass and volume will be the same. So, we can say that in the case of pure water, the value molarity of molality will be equal.