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Osmosis and Osmotic Pressure

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  • Last Updated : 27 Jan, 2022
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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

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. The process of osmosis is stopped if enough pressure is applied on the solution side of the semipermeable membrane. The smallest amount of pressure required to stop the process of osmosis is referred to as osmotic pressure.

Osmotic Pressure

The least pressure required to apply to a solution in order to stop the flow of solvent molecules across a semipermeable membrane is known as osmotic pressure (osmosis). It is a colligative property that is regulated by the concentration of solute particles in the solution. 

To calculate osmotic pressure, use the following formula:

π = iCRT

Where,

π is the osmotic pressure

i is the van’t Hoff factor

C is the molar concentration of the solute in the solution

R is the universal gas constant

T is the temperature

The Dutch chemist Jacobus van’t Hoff proposed this link between a solution’s osmotic pressure and the molar concentration of its solute. 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 SPM in the opposite direction.

Reverse Osmosis Applications

  1. 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.
  2. 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.
  3. 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.
  4. 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

  1. When a substance is immersed in a hypotonic solution, the solvent molecules migrate into the cell, creating turgidity or deplasmolysis. Endosmosis is the term for this process.
  2. When a material is immersed in a hypertonic solution, the solvent molecules escape the cell, causing flaccidity or plasmolysis. Exosmosis is the term for this process.

Effect of Osmosis on Cells

Osmosis has varied effects on different cells. When compared to plant cells, animal cells lyse when placed in a hypotonic solution. The thick walls of the plant cell necessitate more water. When placed in a hypotonic solution, the cells do not explode. A hypotonic solution, in fact, is optimal for a plant cell. An animal cell can only live in an isotonic fluid. In an isotonic solution, the plant cells are no longer turgid, and the plant’s leaves droop. The osmotic flow can be stopped or reversed by adding external pressure to the sides of the fluid, a process known as reverse osmosis. The osmotic pressure is the minimal pressure required to cease solvent transport.

Osmosis and Diffusion Difference

Osmosis

Diffusion

It is only applicable to the 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

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

Examples of Osmosis

  1. Osmosis is the process through which water is absorbed from the earth. Because plant roots have a higher concentration than dirt, water rushes into the roots.
  2. Osmosis affects the plant’s defense cells as well. When water enters the plant cells, the guard cells swell and the stomata open.
  3. When a freshwater or saltwater fish is placed in water with varying salt concentrations, the fish dies as a result of water entering or exiting the animal’s cells.
  4. Osmosis affects humans who are suffering from cholera. The bacteria that overpopulate the intestines reverse the flow of absorption and prevent the intestines from absorbing water, resulting in dehydration.
  5. When the fingers are immersed in water for an extended period of time, the flow of water inside the cells causes them to become pruney.

Sample Problems

Question 1: What are the three different forms of osmotic circumstances that have an impact on live cells?

Solution:

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

Question 2: How is osmosis different from diffusion?

Solution:

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 3: What is the main function of osmosis?

Solution: 

Osmosis aids in the stabilization of the organism’s internal environment by balancing the amounts of water and intracellular fluids. Furthermore, nutrients and minerals enter the cell via osmosis, which is required for cell viability.

Question 4: What is a semipermeable membrane?

Solution:

The semipermeable membrane is a type of biological membrane that allows some molecules or ions to pass through it.

Question 5: What is reverse osmosis?

Solution:

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

Solution:

m = molecular mass of sucrose (C12H22O11) = 342  

w = 5g 

V = 100 mL = 0.1 litre  

S = 0.082,  

T = (15 + 273) = 288 K  

Applying the equation PV = w/m ST,  

P = 5./342 × 1/0.1 × 0.082 × 288 = 3.453 atm

Question 7: The solution containing 10 g of an organic compound per liter showed an osmotic pressure of 1.16 atmosphere at 0° Celsius. Calculate the molecular mass of the compound (S = 0.0821-liter atm per degree per mol.) 

Solution:

Applying the equation  

m = w/PV . ST  

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

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


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