Osmosis - Definition, Mathematical Representation, Types of Solutions, Reverse Osmosis, Practice Problems and FAQ

Have you ever wondered how our blood is purified?

The kidneys filter the water in the blood. The cortex and medulla are the two components of the kidney. The cortex is on the outside, and the medulla is on the inside. Nephrons are the structural and functional units of the kidney. Nephrons are crucial because they assist in the filtering of waste from your blood and transferring it to your urine. The medulla houses the majority of each nephron. The medulla's surroundings have a higher osmotic concentration than the nephron's interior.

You know what it means! It's time for osmosis!

Water goes from inside the nephron tubes to the medulla via a semipermeable membrane. Concentrated urine is eventually left in the nephron. Urine goes from the ureter to the bladder.

TABLE OF CONTENTS

Definition of Osmosis
Definition of Osmotic Pressure
Mathematical Representation
Types of Solutions
Examples of Osmosis in Daily Life
Reverse Osmosis
Practice Problems
Frequently Asked Questions - FAQ

Definition of osmosis

The flow of solvent molecules from a region of higher concentration of solvent to the region of lower concentration of solvent is called osmosis.

Definition of osmotic pressure

The flow of solvent molecules from the solvent side to the solution side across the semipermeable membrane can be stopped if some extra pressure is applied on the solution side. This extra pressure that just stops the flow of solvent is called the osmotic pressure of the solution.

If some extra pressure is applied to the solution side, the flow of solvent molecules from the solvent side to the solution side through the semipermeable membrane can be stopped. The osmotic pressure of the solution is the additional pressure that just stops the flow of solvent.

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Mathematical representation

For dilute solution, it has been found experimentally that osmotic pressure is proportional to molarity C, of the solution at a given temperature T. Thus,

Experimental research has shown that for diluted solutions, osmotic pressure is inversely proportional to the molarity C, of the solution at a given temperature T. Thus,

$Π = C R T$

Where, is the osmotic pressure

R is universal gas constant

$Π = (\frac{n}{V}) R T$

Where V is the volume of the solution in L containing n mol of solute.

If w grams of solute of molar mass M is present in the solution, then

$n = \frac{w}{M}$

We can write,

$Π V = (\frac{w}{M}) R T$

$M = \frac{w R T}{Π V}$

Types of solutions

Isotonic solution: Two solutions having the same osmotic pressure are termed as isotonic solutions.

Isotonic solutions are two solutions that have the same osmotic pressure.

Hypertonic solution: A solution having a higher osmotic pressure relative to some other solution is called a hypertonic solution.

Hypotonic solution: A solution having a lower osmotic pressure relative to some other solution is called a hypotonic solution.

Examples of osmosis in daily life

Relieving sore throat

When you have a sore throat, the excess water in the cells and the surrounding tissues causes the throat to expand. The saltwater you gargle with has a lower concentration of water than the cells of the throat. As a result, water molecules move from the region of lower concentration (swollen throat cells) to the region of higher concentration (saltwater), reducing pain and swelling.

Excess water in the cells and surrounding tissues causes the throat to swell when you have a sore throat. The saltwater you gargle with contains lower concentration water than the cells of your throat. As a result, water molecules move from a low concentration region (swollen throat cells) to a high concentration region (saltwater), relieving pain and swelling.

Soaking resins in water

Resins swell owing to osmosis when soaked in water. By osmosis, water travels from a region of higher water concentration to a region with lower water concentration (resins) until it reaches equilibrium, which occurs when the concentrations of both solutions are equal.

Reverse osmosis

If an external pressure greater than the osmotic pressure is applied, the flow of solvent molecules can be forced to flow in the opposite direction of osmosis i.e. from the solution to the pure solvent. This process is known as reverse osmosis. It is used to desalinate seawater in order to obtain fresh drinking water.

Practice problems:

Question1. The osmotic pressure of a cane sugar solution at 297 K is 2.5 atm. Determine the strength of the solution in mol L^-1.

Solution:

$Π = C R T$

$C = \frac{Π}{R T}$

$C = \frac{2.5}{0.0821 ✕ 297}$

$C = 0.01025 m o l L^{- 1}$

Question2. Find the osmotic pressure of 0.1 M glucose at 300 K ?

Solution:

The formula of osmotic pressure is given by

$Π = C R T$

$= 0.1 ✕ 0.0821 ✕ 300$

$= 2.463 a t m$

Question3. Find the osmotic pressure of a 12% solution of cane sugar (molecular mass = 342) at 290 K?

Solution:

12 g of sugar is dissolved in 100 mL. Thus, 342 g sugar is dissolved in

$\frac{100 ✕ 342}{12 ✕ 1000} = 2.85 L$

$Π = (\frac{n}{V}) R T$

$Π V = n R T$

$Π = \frac{n R T}{V}$

$Π = \frac{1 ✕ 0.0821 ✕ 290}{2.85}$

$Π = 8.35 a t m$

Question4. A solution is prepared by dissolving 0.6 g urea (molar mass =60 g mol^-1) and 1.8 g of glucose (molar mass=180 g mol^-1) in 100 mL of water at 27^oC. The osmotic pressure of the solution is(R=0.0821 L atm K^-1 mol^-1).

Solution:

Number of moles of urea $n_{u r e a} = \frac{0.6}{60} = 0.01$

Number of moles of glucose $n_{g l u c o s e} = \frac{1.8}{180} = 0.01$

$Π = (\frac{n}{V}) R T$

$Π = \frac{n_{u r e a} + n_{g l u c o s e}}{V} R T$

$Π = \frac{0.01 + 0.01}{100} ✕ 1000 ✕ 0.0821 ✕ 300$

$Π = 4.92 a t m$

Frequently Asked Questions - FAQ

Question1. How does reverse osmosis work?
Answer: Reverse Osmosis works by using a high-pressure pump to increase the pressure on the salt side of the RO and force the water across the semipermeable RO membrane, leaving almost all (around 95 to 99 percent) dissolved salts in the reject stream behind.

Reverse osmosis works by increasing the pressure on the salt side of the RO and forcing the water across the semipermeable RO membrane, leaving almost all (around 95 % to 99 %) of the dissolved salts in the reject stream behind.

Question2. What is a semipermeable membrane?
Answer: The semipermeable membrane is a biological or synthetic membrane, which functions by permitting the movements of certain molecules or ions to pass through it.

Question3. How to save eyes from dry contact lenses?
Answer: Soft contact lenses consist of semipermeable materials. If you wear contacts after storing them in sterile saline solution, the concentration of saline in the contact lenses matches the salt content in the natural fluid that moistens your eyes. The contact lenses stay moist, soft and comfortable. If you store contact lenses in distilled water, the salt concentration is higher in the eye fluid and water flows out of the contact lenses slowly drying them out.

Semipermeable materials make up soft contact lenses. When you wear contacts after soaking them in sterile saline solution, the concentration of saline in the lenses matches the salt content of the natural fluid that keeps your eyes moist. The lenses remain moist, soft, and comfortable. When contact lenses are stored in distilled water, the salt concentration in the eye fluid increases and water flows out of the contact lenses, slowly drying them up.

Question4. What are the differences between diffusion and osmosis?

Answer:

Osmosis	Diffusion
It involves the movement of solvent molecules	It involves movement of solute molecules
It occurs only across a semipermeable membrane	It does not require a semipermeable membrane.
Example: shrinking of potato slice when kept in the sucrose solution.	Example: A tea bag immersed in a cup of hot water will diffuse into water and change its colour.