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Osmosis and Osmotic Pressure

Last Updated : 02 May, 2023
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A solution is a homogeneous mixture of two or more particles having particle sizes smaller than one nanometer. Sugar and salt solutions in water, as well as soda water, are common examples of solutions. In a solution, all of the components appear as a single phase. There is particle homogeneity, which means that the particles are evenly dispersed. This is why a full bottle of soft drink tastes the same.

The component that dissolves the other component is known as the solvent. Solute refers to the component(s) that are dissolved in the solvent (s). In general, the solvent is present in greater proportion than the solute. The solute amount is less than the solvent amount. Solutes and solvents can exist in every state of matter, including solids, liquids, and gases. A liquid solution is composed of a solid, liquid, or gas dissolved in a liquid solvent. Solid and gaseous solutions are represented by alloys and air, respectively.


Osmosis is the process of moving solvent molecules from a low solute concentration area to a high solute concentration area through a semipermeable membrane. Eventually, an equilibrium between the two sides of the semipermeable membrane is formed (equal solute concentration on both sides of the semipermeable membrane). Because the semipermeable barrier only allows solvent molecules to pass through, no solute particles can pass through. 

Note: Osmosis is discovered and named by the French physiologist Henri Dutrochet. He also invented osmometer, a device used to measure osmotic pressure.

Osmotic Pressure

Osmotic Pressure is the least pressure required if applied to a solution, the inward flow of solvent molecules across the semipermeable membrane is stopped. It is a colligative property that is regulated by the concentration of solute particles in the solution. 

Process of Osmosis


Osmotic Pressure Formula

The Dutch chemist Jacobus van’t Hoff proposed this link between a solution’s osmotic pressure and the molar concentration of its solute. which is as follows:

∏ = iCRT


is the osmotic pressure,

i is the van’t Hoff factor,

C is the molar concentration of the solute in the solution, (C=n/V; where n is the number of moles and V is the volume.)

R is the ideal gas constant,

and T is the temperature in Kelvin

It should be noted that this equation only applies to solutions that act like perfect solutions.

Reverse Osmosis

The minimal pressure required to stop the passage of the solvent across the semipermeable membrane is referred to as osmotic pressure. When a pressure greater than the osmotic pressure is applied to the solution side (the side with a high solute concentration), the solvent particles on the solution side move through the semipermeable membrane to the area with a low solute concentration. Reverse osmosis refers to the flow of the solvent through the semipermeable membrane in the opposite direction.

Application of Reverse Osmosis

  • Electronic component manufacturers require the finest quality water possible. Reverse osmosis is commonly used to remove the majority of contaminants from a water supply before it is introduced into a polishing ion exchange system. Reverse osmosis increases the life of the ion exchange beds while lowering the overall cost of producing huge volumes of high-quality water.
  • Depending on the nature of the chemical production process, the maker of chemicals requires varied grades of water. In some circumstances, reverse osmosis water will yield satisfactory product water on its own, and it is utilized as a pre-treatment when greater qualities are required.
  • In this business, reverse osmosis has been used successfully to not only purify water for use in plating solution makeup water and drag out baths but also to concentrate important plating metals in the waste stream for recycling in a closed-loop process.
  • On a small and large scale, reverse osmosis is widely utilized in the desalting sea or brackish water for potable consumption. Because of its low energy requirements, the technique is particularly appealing in this application.

Types of Osmosis

There are two types of Osmosis that take place in the cells of animals as well as plants, those are as follows:


When a substance is immersed in a hypotonic solution, the solvent molecules migrate into the cell, creating turgidity (swollen) or deplasmolysis. This process is called Endosmosis.


When a material is immersed in a hypertonic solution, the solvent molecules escape the cell, causing flaccidity or plasmolysis. This process is called Exosmosis.

Effect of Osmosis on Cells

In biological, systems osmosis is very essential as many biological membranes are semipermeable. For example in an animal cell, if surrounded by a hypertonic environment (outside the cell is higher water concentration) then due to osmosis water leaves the cell and the cell shrinks, opposite to it if surrounded by the hypotonic surroundings (outside the cell with lower water concentration) then water diffuses into cells and causes the cell to swell. Animal cells can only live if it is surrounded by an isotonic solution. The same effect of hypertonic and hypotonic solutions can be seen in plants cell.

Effect of hypertonic, isotonic, hypotonic solution on plant and animal cell


Difference between Osmosis and Diffusion

Osmosis can seem like diffusion but there are a lot of differences between both which are as follows:



It is only applicable to liquid media. It can be found in a variety of liquids, gases, and even solids.
A semipermeable membrane is required. Doesn’t require a semi-permeable membrane.
This is determined by the number of solute particles dissolved in the solvent. It is affected by the presence of other particles.
Water is required for particle mobility. The mobility of particles does not require the use of water.
Only the solvent molecules can diffuse. Solute and solvent molecules can both disperse.
Particles can only flow in one direction. The movement of particles occurs in all directions.
The entire process can be stopped or reversed by applying extra pressure to the solution side. This process cannot be halted or reversed.
This only happens amongst solutions that are similar in nature. Occurs between solutions that are similar and solutions that are dissimilar.
Only water or another solvent goes from a high-energy or concentration zone to low energy or concentration region. Any substance can migrate from a location of high energy or concentration to a region of low energy or concentration.

Significance of Osmosis

  • Nutritional supply and the discharge of metabolic waste products are both affected by osmosis.
  • It is in charge of absorbing water from the earth and transporting it to the plant’s higher portions via the xylem.
  • It maintains the equilibrium of water and intercellular fluid levels in a living organism’s interior environment.
  • It keeps the turgidity of cells.
  • It is the method by which plants maintain their water content in the face of continual water loss owing to transpiration.
  • This process regulates water transport from cell to cell.
  • Osmosis causes cell turgor, which regulates plant and plant component mobility.
  • Osmosis is also responsible for the dehiscence of fruits and sporangia.
  • Higher osmotic pressure protects plants against drought damage.

Examples of Osmosis

There are a lot of examples of Osmosis in nature as Osmosis is a very essential part of life. Some of the examples are as follows:

  • The process through which water is absorbed from the soil is also because of osmosis as water rushes into the roots because plant roots have a higher concentration than soil.
  • Osmosis also impacts the plant’s defense cells. The guard cells enlarge and the stomata open as water enters the plant cells.
  • A freshwater or saltwater fish dies as a result of water entering or departing the animal’s cells when placed in water with different salt concentrations.
  • Humans suffering from cholera are also affected by osmosis as the overpopulation of bacteria in the intestines reverses the absorption flow and prevents the intestines from absorbing water, resulting in dehydration.

Solved Examples of Osmotic Pressure

Question 1: Calculate the osmotic pressure of 5% solution of cane sugar (sucrose) at the temperature of 15° Celsius.


m = molecular mass of sucrose (C12H22O11) = 342 amu  

w = 5g 

V = 100 mL = 0.1 litre  

we know, R = 0.0821 L⋅atm⋅K−1⋅mol−1,  

T = (15 + 273) = 288 K  

and as glucose is the non-ionic compound and doesn’t dissociate to give any ions in the solution, it’s van’t Hoff factor is 1.

Rearranging ∏ = iCRT, we get ∏V = w/m ⋅RT,  

∏ = 5/342×1/0.1 × 0.082 × 288 = 3.453 atm

Question 2: The solution containing 10 g of an organic non-ionic compound per liter showed an osmotic pressure of 1.16 atmosphere at 0° Celsius. Calculate the molecular mass of the compound (S = 0.0821 L⋅atm⋅K−1⋅mol−1


As compound is non-ionic, it’s van’t Hoff factor is 1.

Applying the equation  m = w/∏V ⋅RT  

Given w = 10 g, P = 1.18 atm, V = 1 litre, S = 0.0821 L⋅atm⋅K−1⋅mol−1 and T = 273 K.  

m = 10/1.18×1 × 0.0821 × 273 = 189.94 amu  

FAQs on Osmosis and Osmotic Pressure

Question 1: What is Osmosis?


Osmosis is the process of moving solvent molecules from a low solute concentration area to a high solute concentration area through a semipermeable membrane. Some examples of osmosis are the swelling of resins when left in water for some time, the pruning of fingers after putting them in water for some time, etc. 

Question 2: What is reverse osmosis?


Reverse osmosis is a natural phenomena that takes place in the opposite direction of natural osmosis. This type of osmosis is used to remove the bulk of pollutants from water by forcing the water through a semi-permeable membrane under pressure.

Question 3: How many types of Osmotic solutions?


There are three kinds of osmotic solutions:  isotonic, hypertonic and hypotonic.

A pair of two solutions with same osmotic pressure at a given temperature are called isotonic solutions.

For two solutions, one with higher osmotic pressure and one with lower osmotic pressure compared to each other, solution with higher osmotic pressure is hypertonic solution with respect to the other solution and solution with lower osmotic pressure is called hypotonic solution with respect to the other solution.

Question 4: How is osmosis different from diffusion?


Osmosis is the movement of solvents through a semi-permeable membrane from a low-solute-concentration region to a high-solute-concentration region. Diffusion, on the other hand, does not require a semi-permeable membrane to occur, as molecules migrate from a location of higher concentration to a region of lower concentration.

Question 5: What is a semipermeable membrane?


The semipermeable membrane is a type of biological membrane that allows some molecules or ions to pass through it and blocks the remaining of them.

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