Osmotic Pressure Equation - Definition, Formula, Applications, FAQs

Osmotic pressure is basically the concept of biology and chemistry in which we study how pressure is required to stop the flow of solvent through a membrane called a semipermeable membrane. A semipermeable membrane is a membrane that allows some molecules to pass through them while not allowing the big molecules. The osmosis of the P phenomenon occurs when the movement of solvent molecules occurs from the area of lower Concentration to the higher concentration through that semipermeable membrane in order to balance the Concentration on both sides. Osmotic pressure is that pressure which is needed to prevent the flow of solvent into the more concentrated solution. It can be also called the back pressure that is needed to stop the osmosis.

Osmosis was first discovered by the French physiologist Rene Dutrochet in the early 1800s and was awarded for his discovery. He discovers it by studying the movement of water in the plant tissue and the effect of different solutions on this tissue. His observation is the main framework for further studies as he noted that the water can be passed through the membrane as well to balance the concentration on both sides.
Then the term osmosis was given by the British Chemist Thomas Graham in 1854 who further developed this concept of osmosis. There are several factors that affect the process of osmosis such as the temperature, the nature of the solute, and mainly the concentration of the solute as a higher concentration of solute leads to higher osmotic pressure which is needed to counteract the osmotic flow. An increase in temperature leads to an increase in the motion of particles of solvent which results the more intense osmosis. The nature of solute affects it as its dissociation in ions effectively increases the solute concentration

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Osmosis and Osmotic Pressure

Osmosis: It is the flow of solvent molecules from a solution of low concentration to a solution of higher concentration when they are separated by a semi-permeable membrane(SPM), the concentration obviously being defined with respect to the solute.

Semi-permeable membrane consists of a network of submicroscopic pores or holes. The pore size is such that the smaller solvent molecules can move across the membrane while the movement of larger solute molecules is hindered by the smaller pores of the SPM.

There are many phenomena which include the process of osmosis that we observe in daily lives. For example, raw mangoes shrivel when pickled in brine (saltwater); wilted flowers revive when placed in freshwater, blood cells collapse when suspended in saline water, etc.

Assume that only solvent molecules can pass through these semipermeable membranes. If this membrane is placed between the solvent and solution as shown in figure given below, the solvent molecules will flow through the membrane from pure solvent to the solution. This process of flow of the solvent is called osmosis.

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The flow will continue till the equilibrium is attained. This flow of the solvent molecules to the solution side across a semipermeable membrane can be stopped if some extra pressure is applied on the solution. This pressure that just stops the flow of solvent is called osmotic pressure of the solution. The osmotic pressure is represented by the letter (Pi).

This is illustrated in Figure given below. The osmotic pressure of a solution is the excess pressure that must be applied to a solution to prevent osmosis, i.e., to stop the passage of solvent molecules through a semipermeable membrane into the solution.

Osmotic pressure is a colligative property as it depends on the number of solute molecules and not on their identity. For dilute solutions, it has been found experimentally that osmotic pressure is proportional to the molarity, C of the solution at a given temperature T. Thus:

$\mathrm{\Pi }=CRT$

Here П is the osmotic pressure and R is the gas constant. The above equation can also be written as

$\mathrm{\Pi }=\left(\frac{n_2}{V}\right)RT$

Here V is the volume of a solution in litres containing n2 moles of solute.

If w₂ grams of solute, of molar mass, M₂ is present in the solution, then ${\mathrm{n}}_2={\mathrm{w}}_2/{\mathrm{M}}_2$ and we can write,

$\mathrm{\Pi }V=\frac{W_{2}RT}{M_2}$

Thus $M_2=\frac{W_{2}RT}{\mathrm{\Pi }V}$

Thus, knowing the quantities w₂, T, П and V we can calculate the molar mass of the solute.

Related Topics Link,

• Mixtures
• Solute
• Solution Properties Concentration
• Relation Between Molarity And Molality
• Ideal Solution

Recommended topic video on(osmotic pressure)

Some Solved Examples

Example.1

1. In osmosis reaction, the volume of solution:

1)Decreases slowly

2) (correct)Increases slowly

3)Suddenly increases

4)No change

Solution

Osmosis -
The spontaneous flow of solvent molecules from pure solvent to the solution through the semi-permissible membrane is known as osmosis.
Osmosis reaction takes place when the volume increases.

Hence, the answer is the option (2).

Example.2

2. If the molecular weight of the compound is increased then sensitivity is decreased in which of the following methods:

1)Elevation in boiling point

2)Viscosity

3)Osmosis

4) (correct)Dialysis

Solution

Osmosis -
The spontaneous flow of solvent molecules from the pure solvent to the solution through the semi-permeable membrane is known as osmosis.
According to the dialysis process, molecular weight increases but sensitivity decreases.

Hence, the answer is the option (4).

Example.3

In osmosis:

1)Solvent molecules move from higher concentration to lower concentration

2) (correct)Solvent molecules move from lower to higher concentration

3)Solute molecules move from higher to lower concentration

4)Solute molecules move from lower to higher concentration

Solution

In osmosis, solvent molecules move from a solution of lower concentration to a solution of higher concentration.

Hence, the answer is the option (2).

Example.4

4. Osmotic pressure is 0.0821 atm at a temperature of 300K . Find concentration in mole/liter

1)0.033

2)0.066

3) (correct)$0.33\times {10}^{-2}$

4)3

Solution

$\pi =CRT,C=\frac{\pi }{RT}=\frac{0.0821}{0.821\times 300}=0.33\times {10}^{-2}$

Hence, the answer is the option (3).

Example.5

5. Osmotic pressure of a solution containing 0.1 moles of solute per liter at 273 K is (in atm)

1) (correct)2.24

2)22.4

3)4.48

4)44.8

Solution

$\begin{array}{rl}& \pi =CRT\\ & \pi =\frac{w}{m}\times RT=\frac{0.1}{1}\times 0.0821\times 273=2.24\end{array}$

Hence, the answer is (2.24).

Example.6

6. If 3 gm of glucose (mol. wt. 180) is dissolved in 60 gm of water at 15⁰C . Then the osmotic pressure (in atm ) of this solution will be

1) (correct)6.57

2)0.34

3)0.65

4)5.57

Solution

$\pi =CRT=\frac{3\times 1000}{180\times 60}\times 0.0821\times 288=6.56\mathrm{atm}$

Hence, the answer is (6.56 atm).

Summary

Osmotic pressure is very beneficial as it has various applications in various fields such as it has various applications in the medical field, in biology and medicine, also in the food industry, in industrial processes. In the medical field dialysis is the main and very important aspect of it in this the osmotic pressure is utilized to remove the waste product from the blood of a patient with kidney failure. It is also important to maintain the isotonic Solutions means the balance of fluid in the body of the patient. Reverse osmosis is very important and used to desaline the water means to purify the water by pushing a semipermeable membrane removing salt and contaminants. Osmosis is also important for the functioning of cells to regulate the movement of water in and out of cells influencing the shape of the cell and its volume. it is also used to preserve the food by drawing out the water from them such as salt and sugar so that they can be stored for a long period. Osmosis also helps in controlling the concentration of reaction for the industrial process. osmotic pressure also play an important role in the irrigation process for improving water content in soil

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