Short Notes On Osmotic Pressure

Osmotic pressure can be understood as the amount of pressure required to control the flow of a solvent through a barrier. In this case, the barrier is a semipermeable membrane. A semipermeable membrane will have tiny pores sufficient to allow the solvent movement between two different solutions. Each solution will naturally have different concentration levels, and the osmotic pressure required to prevent the flow of solvents will differ accordingly. Osmotic pressure can be calculated using this formula: π = icRT

where

π is the osmotic pressure

i is the dimensionless van’t Hoff factor

c is the molar concentration of solute

R is the ideal gas constant

T is the absolute temperature (usually in kelvins). 

Osmosis

In order to understand osmotic pressure, it is important to know the process of osmosis. The word ‘osmosis’ originates from the Greek work ōsmos, which means to thrust or push. Osmosis is the movement of water from one region to another through a semipermeable membrane. This can also be called the movement of solvent molecules from one solute to another. Generally, the solvent molecules move from the solute with a lower concentration to the solute with a higher concentration until a state of equilibrium is achieved.

As the water movement across the membrane increases, the osmotic pressure needed to prevent the flow increases eventually. 

Let us understand this phenomenon with an example. Imagine a U-shaped tube where we fill water on the left and dilute glucose solution on the right. The point where they initially meet would be the semipermeable membrane. Now, the water will intend to move from a lower concentration solution to a higher concentration one. Thus, the net flow of water will occur through a membrane until equilibrium is achieved. At this stage, osmotic pressure is applied to prevent water flow through the membrane. 

Practical Applications of Osmotic Pressure

Plants

Osmotic pressure can be commonly seen in plants. The leaves and stems of some plants get dry and sag quickly if they run out of water. In these cases, if they are provided with sufficient water, they quickly absorb it and bulge. The process that causes this is osmosis, making water flow to the salts 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. In this manner, osmotic pressure plays an essential role in plant growth.  

Human Body

Osmotic pressure is also crucial in human bodies. When we have sufficient water intake, the water runs through the bloodstream and diffuses into cells through osmosis. However, if the water intake is less, the water inside our body moves into the blood, increasing the salt concentration in our body. This condition can directly affect the cell function, causing dehydration. The right amount of osmotic pressure occurs when there is enough water intake, resulting in a healthy life.

Calculation of Osmotic Pressure

Osmotic pressure can be calculated using this formula: π = icRT

This formula can be applied to calculate the osmotic pressure when the solution is considered ideal, that is, when the solute concentration is low. 

In the formula, c is the molar concentration of the solute, that is, the original number of atoms, ions, or molecules present in the solute. Notably, the number of particles determines their interaction in osmosis. R is the ideal gas constant. In this case, it also refers to liquids such as water. T refers to the temperature in Kelvin. 

The osmotic pressure of a solution can be increased by increasing its temperature. Temperature, in this scenario, refers to the measure of energy in molecules. The osmotic pressure of a solution can be increased by increasing the number of solute molecules. 

Another formula for calculating osmotic pressure is π = n/VRT where V is the volume of water.        

Example Question

Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of the molar mass 185,000 in approximately 450 mL of water at 37 °C.

Given data:

Mass of polymer = 1.0 g

Molar mass = 185,000

Volume of water = V = 450 mL = 0.45 L

Temperature = (37 + 273) K = 310 K

Osmotic pressure can be calculated by

ℿ = n/v.RT

On deriving, we get,

π = 30.95 Pa

Conclusion

Through this article, we learned the process of osmosis and osmotic pressure. Osmotic pressure is the minimum pressure applied to prevent the flow of a solvent through a semipermeable membrane from a low concentrated solute to a high concentrate solute. There are numerous real-world applications of osmotic pressure, such as in plants and human beings. We learnt in detail how this process helps keep plants alive and healthy. We also studied how the process of osmotic pressure is inevitable in saving humans from dehydration and other related physical issues. Osmotic pressure can be calculated with the formulas  π = icRT and π= n/v.RT