Osmotic Pressure: Definition, Formula, Examples, Description, Types, Measurement

What Is Osmotic Pressure?

Osmotic pressure is the minimum pressure that must be applied to a solution to stop the flow of solvent molecules through a semipermeable membrane—osmosis. It is colligative in nature and dependent on the concentration of the solute particles in the solution. Osmotic pressure can be worked out with the help of the following formula:

π = iCRT

Where,

π is the osmotic pressure

i is the van't Hoff factor

C is the concentration of the solute in moles per unit volume of solution

R is the universal gas constant

T is the temperature

The Dutch chemist Jacobus Van't Hoff proposed the following relationship of the osmotic pressure of a solution with the molar concentration of its solute. Note that the equation holds for an ideal solution.

What Is Osmosis?

Osmosis can be defined as the flow of solvent molecules through a semipermeable membrane from a space with a low solute concentration to one with a high solute concentration. This occurs until equilibrium is achieved across the semipermeable membrane, with equal concentration on both sides.

Important note: The semipermeable membrane allows the movement of only solvent molecules through it – solute particles cannot pass through it.

If sufficient pressure is applied to the solution side of the semipermeable membrane, the process of osmosis gets stopped. The minimum pressure that is required to just stop the process of osmosis is known as osmotic pressure.

Mechanism Of Osmotic Pressure

Osmotic pressure develops because of the flow of solvent molecules from an area with a low concentration of solute to an area with a high concentration of solute to attain equilibrium. This movement then creates a pressure differential.

Explanation Of How Osmotic Pressure Develops

Osmotic pressure develops due to the movement of the solvent molecules from an area of low concentration of solutes to one with a high concentration of solutes to establish equilibrium. This move produces pressure, which should be balanced to halt the flow of a solvent.

Factors Affecting Osmotic Pressure

• Solute Concentration:

The higher the concentration of the solute, the higher the osmotic pressure.

• Temperature:

The kinetic energy of molecules increases with the temperature rise, and this, in turn, increases the osmotic pressure.

• Nature of Solute:

An ideal condition, however, exists because all solutes affect osmotic pressure differently due to variance in their dissociation in solution.

Mathematical Expression

The Van't Hoff mathematical expression, π = iCRT, expresses the relationship between osmotic pressure and the concentration of solutes. This mathematical relationship focuses on the fact that osmotic pressure is directly proportional to the number of solute particles in concentration.

Tonicity And Osmotic Pressure

Tonicity refers to the extent to which a solution causes a cell to swell or shrivel. It is determined by the osmotic pressure.

Definition Of Tonicity

Tonicity refers to the relative concentration of solutes in the solution outside a cell compared to that inside the cell.

Solution Types

• Hypertonic: This is the solution where the concentration of solutes outside the cell is high due to which the cell loses water and shrinks.

• Hypotonic: A solution with a reduced concentration of solutes outside the cell, which means that it will gain water and swell.

• Isotonic: The concentrations of the solutes are equal inside and outside the cell; there is no net movement of water.

Effects On Cells In Different Tonicity

• Hypertonic Solutions: Because of the loss of water, the cells shrink.

• Hypotonic Solutions: Cells become turgid, may swell and possibly burst due to water intake.

• Isotonic Solutions: Cells retain their shape, for no net movement of water takes place.

Osmotic Pressure In Plants

The osmotic pressure plays an important role in maintaining the structure and working of plants.

Role In Plant Turgor Pressure

Turgor pressure is the pressure the cell membrane exerts on the cell wall and is facilitated by osmotic pressure. It helps in maintaining the posture of the plant upright.

Role In Maintenance Of Plant Structure

Sufficient water supply that maintains cells in a turgid state, supports the upright position of the plant. A lack of water causes wilting due to a lack of turgor in the cells.

Osmosis Working Field In Plant Cell

• Absorption of Water by Roots: The roots of a plant absorb water from the soil due to osmosis, which forms part of the total water intake of the plant.

• Cell Expansion: Osmotic pressure allows the plant cells to take in water and expand; this can be associated with plant growth.

Applications Of Osmotic Pressure

There exist several applications of osmotic pressure in practical life.

Inverse Osmosis

Water Purification: Because of the pressure exerted that is greater than the osmotic pressure, reverse osmosis removes the impurities from water, whether inorganic or organic compounds, viruses, bacteria, and other microorganisms, by forcing the water molecules through a semipermeable membrane.

Seawater Desalination: It makes seawater as fresh as water; that is, it makes seawater free from dissolved salts and other contaminants.

Medical Applications

Intra Venous Fluid Administration: Intravenous fluids must always be isotonic to the blood to avoid disrupting the cells.

Dialysis: In renal failure, dialysis machines use the principles of osmosis to remove waste products from the blood.

Preservation Of Food

Water Activity Reduction: It is through osmotic pressure that water is drawn out of food, and in the process, microbial growth is reduced, allowing the food to be stored for a longer time.

Osmotic Pressure Measurement

Osmotic pressure can be measured using special instruments and techniques.

Methods Of Measurement

• Osmometer: An osmometer is a device used to calculate the osmotic pressure either by measuring the freezing point depression of a solution or by vapour pressure.

• Practical Considerations: For accurate measurement, the temperature and concentration should be controlled very tightly.

Factors Affecting Osmotic Pressure

Several variables will affect the osmotic pressure.

• The Gradient Of Concentration: The more prominent the gradient, the greater will the osmotic pressure be. In other words, if there is a steep gradient in concentration across a semipermeable membrane, then high osmotic pressure would be produced.

• Temperature: With increasing temperature, the kinetic energy of molecules increases affecting osmotic pressure.

• Type Of Solute: The dissociation of solutes into ions can increase osmotic pressure.

Osmotic Pressure And Human Health

Maintaining appropriate osmotic pressure is vital for human health.

Importance In Maintaining Cell Homeostasis

Osmotic pressure regulates the balance of fluids inside and outside cells, ensuring proper cell function and homeostasis.

Conditions Related To Osmotic Pressure Imbalances

• Dehydration: If the consumption of water is low, then the osmotic pressure of the body fluids will be high. This causes the cell to lose water and shrink.

• Edema: Too much fluid in the body decreases the osmotic pressure in body tissues and leads to swelling.

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