Shrinithi Mahadevan


Osmotic Pressure Study Guide

A force that opposes osmosis is a useful attribute that can be used in various situations.


Almost every poet can't help but praise the beauty of grown flowers in their poetry. A tulip garden is definitely a peaceful sight to see. As we all know, plants are living beings, and we can usually see them standing on their own, as they are an important part of our environment. But have you ever wondered how these plants manage to stay upright? Plants do not have bones to sustain their structure, like humans do. Osmotic pressure, a colligative property of solution, can answer this question.

Osmotic Pressure Source


Colligative properties of solutions are determined by the concentration of solute molecules or ions and not by the identification of the solute. Vapor pressure reduction, boiling point elevation, freezing point depression, and osmotic pressure reduction are all examples of colligative qualities. These are the properties of solutions that are not dependent on the identity of the solute but are dependent on the concentration of the solute molecules. The overall flow or passage of solvent molecules over a semipermeable membrane (one that allows the diffusion of particular molecules or ions through it ) through which solute molecules cannot pass is called osmosis. A net movement of solvent into the solution side of the membrane occurs when a sample containing both solute and solvent molecules is introduced on one side of the membrane, and the pure solvent is poured on the other.

Note: Solute particles cannot flow through the semipermeable barrier since it only permits solvent molecules to flow across.

Osmotic-Pressure Source


The osmotic pressure is the minimum pressure required to prevent the inward movement of a solution's pure solvent across a semipermeable barrier. It can also be described as a measurement of a solution's tendency to absorb a pure solvent via osmosis.

                                  π = MRT


pi (π) is the osmotic pressure

M is the molar concentration

R is the gas constant

T is the temperature


Filtration ("reverse osmosis"), a typical water treatment method, is based on osmotic pressure. This is an extensively used water purification technology and is based on osmotic pressure. The filtered water is deposited in a chamber and subjected to a force greater than the osmotic pressure exerted by the water and any dissolved solutes.


  • The passage of solvent molecules through a semipermeable membrane from a low to a high solute concentration region is referred to as osmosis.

  • The osmosis process can be stopped if enough stress is put to the solution side of the semipermeable membrane. This stress is called osmotic pressure.

  • The following formula can be used to estimate osmotic pressure:

                                    π = MRT


1. How do electrolytes affect colligative properties?

Electrolytes dissociate to add more solutes to the solution, changing the colligative characteristics significantly.

2. What are the colligative properties that explain why electrolytes have abnormally high values of colligative properties?

The properties of solutions that are not dependent on the identity of the solute but are dependent on the concentration of the solute molecules are termed colligative properties. Because the solute breaks down into ions in an electrolyte solution, the quantity of particles is higher, and the impact on colligative qualities will be higher as the number of ions increases.

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  1. Osmotic pressure: https://www.ck12.org/c/chemistry/electrolytes-and-colligative-properties/enrichment/Osmotic-Pressure-%C3%8F%C2%80-MRT-Example-2/. Accessed 24 Feb 2022.
  2. Osmotic Pressure: http://pharmaceuticalmicrobiologi.blogspot.com/2017/01/osmotic-pressure.html. Accessed 24 Feb 2022.