Osmotic Pressure: Definition, Notes, Applications, & Examples

Osmosis is defined as the flow of solvent molecules from a pure solvent to a solution across the membrane. The external pressure applied to a solution to prevent the flow of pure solvent across a semipermeable membrane to the solution is osmotic pressure.

Osmotic pressure is defined as the minimum pressure needed to prevent the inward flow of a solution’s pure solvent through a semipermeable membrane. It is a colligative property of solutions which measures the pressure required to prevent a solvent's flow into a solution through a semipermeable membrane. It arises from the tendency of solvent molecules to move from an area of lower solute concentration to an area of higher solute concentration through a semipermeable membrane to equalise the concentration on both sides of the membrane.
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Dutch chemist Jacobus Van’t Hoff proposed the relationship between the osmotic pressure of a solution and the molar concentration of its solute. The mathematical relationship between osmotic pressure (π), solute concentration (c), and the gas constant (R) is described by the Van't Hoff equation, also known as the osmotic pressure formula.

π = icRT
Where:

• π is the osmotic pressure
• c is the molar concentration of the solute in solution (in moles per litre)
• R is the ideal gas constant
• T is the absolute temperature (in Kelvin)
• i is the Van't Hoff factor.

Note that Van't Hoff equation is applicable for the solutions which behave like ideal solutions.

Semipermeable Membrane: Osmosis occurs through a semipermeable membrane that allows the passage of solvent molecules but not solute molecules. Common examples of semipermeable membranes include cell membranes and certain synthetic membranes.

Concentration Gradient: Osmotic pressure is directly proportional to the difference in solute concentration between the two sides of the membrane. The greater the difference in solute concentration, the higher the osmotic pressure.

Units: Osmotic pressure is typically measured in units of pressure, such as pascals (Pa) or atmospheres (atm).

Importance: Osmotic pressure is a crucial concept in biology and chemistry. In biological systems, it plays a role in processes like the movement of water in and out of cells. In chemistry, it is used to determine the molar mass of unknown solute particles in a solution through experiments.

Colligative Property: Osmotic pressure is considered a colligative property because it depends on the number of solute particles rather than their chemical nature. For example, a solution of sugar (a non-ionic solute) and a solution of salt (an ionic solute) will exert the same osmotic pressure if they have the same concentration of solute particles.

• Osmotic pressure is used in water purification. This process is applicable in wastewater remediation and extracting salt from seawater.
• Osmometry is used to determine the molecular mass of polymers. 
• Osmotic pressure is commonly seen in plants. The leaves and stems of plants become dry and sag soon if they run out of water. In such cases, if we provide sufficient water, plants quickly absorb it and bulge. The process that causes this is osmosis, making water flow into the salt in plant cells. The cells, in turn, inflate and grow healthy. This is a continuous process observed during plant growth. As the cells absorb more water, they ensure healthy plant growth. Thus, osmotic pressure plays a key role in plant growth. 
• Osmotic pressure plays an important role in maintaining cell homeostasis.
• The measurement of osmotic pressure is used to determine molecular weights of compounds.

Osmotic pressure occurs becase of osmosis. The real world example of osmotic pressure is mentioned below.

• Palnt Turgor (Maintaining Plant Structure)
• Food preservation
• Kidney Dialysis
• Reverse Osmosis (Water Purification)
• Dehydration and Rehydration in Humans
• Red Blood Cells in different solutions