Education Journalist | Study Abroad Lead
Osmolarity is the way of expressing the concentration that reflects the osmoticity of the given solution. When the concentration is expressed as osmoles per liter of the solution, it is called osmolarity. It is Osm/L or mOsm/L.
- The solute in the solution should be osmotically active, they should cause the movement of water across a cell membrane via osmosis.
- The dissociated ions in a solution are measured as Osmoles and contribute to somatic pressure.
- Osmolarity is given by the formula= No. of osmoles (osmol) / Volume of solution (in L).
| Table of Content |
Key Terms: Osmolarity, Concentration, Solution, Solute, Cell membrane, Osmosis
What is osmolarity?
[Click Here for Sample Questions]
Osmolarity is the concentration expressed as osmoles per liter of the solution. Osmolarity is given by the formula= No. of osmoles (osmol) / Volume of solution (in L). Now let us calculate the osmolarity:
If in 400 ml of water in which 60g of magnesium chloride (MgCl2) is dissolved. To calculate osmolarity for the above information:
- The atomic mass of Mg is 24.3 and that of Cl is 35.5.
- Calculate the weight in grams of one mole of MgCl2 = 24.3 +35.5 + 35.5 = 95.3 g.
- Convert grams into moles: No. of grams in the solution by the atomic mass of the solute. 60g/95.3g which is 0.63 moles of magnesium chloride.
- Calculate how many osmoles can be found in your 400 ml solution, multiply moles 0.63 by osmoles 3 = 1.89 osmoles of solute in 400 ml of water.
- The formula for osmolarity is osmoles per liter. Therefore, divide 1.89 osmoles by 0.4L.
- The osmolarity of the solution is 4.73 Osm/L
Types of solute
[Click Here for Previous Year Questions]
Osmolarity is distinct from molarity/ It is related to colligative properties like vapor pressure, freezing point depression, and boiling point elevation. A solute is a substance that is dissolved in a solution. In a liquid solution, the amount of solvent is greater than the amount of solute added to form a solution. There are three types of solute:
- Liquid
- Solid
- Gas
Read more: Solubility
What is Diffusion?
[Click Here for Sample Questions]
For a better understanding of osmolarity, we first have to understand how the movement of solute takes place in a solution. The movement of molecules from an area of higher molecule concentration to a lower concentration is called diffusion.
- It is a passive process which means no ATP is required for the process of diffusion.
- If we talk about osmosis, it is a type of diffusion, that takes place through a semi-permeable membrane.
- But in the case of diffusion, a semi-permeable membrane is not required.
Read more: Diffusion formula
What is Osmosis?
[Click Here for Previous Year Questions]
Osmosis is the movement of solvent molecules through a selectively permeable membrane. It should be noted that in osmosis, the solute does not diffuse. It occurs across a concentration gradient that is from higher to lower concentration. In the case of the human body, it is the concentration of water molecules that is present on both sides of the semi-permeable cell membrane.
Depending on the concentration across the membrane, there are three types of solutions:
- Isotonic solution
- Hypotonic solution
- Hypertonic solution
Things to Remember
- Osmolarity is the concentration expressed as osmoles per liter of the solution.
- Osmolarity is given by the formula= No. of osmoles (osmol) / Volume of solution (in L)
- Osmosis is the process of movement of a solvent across the concentration gradient with the requirement of energy.
- Osmolarity is expressed as Osm/L or mOsm/L
- Depending on the concentration across the membrane, there are three types of solutions: Isotonic, hypotonic, and hypertonic solution
- In the case of diffusion, a semi-permeable membrane is not required.
- Diffusion is a passive process which means no ATP is required for the process of diffusion.
Previous Year Questions
- Extraction of metal from the ore cassiterite involves...[JEE Advanced 2011]
- Commonly used vectors for human genome sequencing are...[NEET UG 2014]
- Interfascicular cambium and cork cambium are formed due to..
- Pneumotaxic centre is present in...[UP CPMT 2007]
- Reaction of HBr with propene in the presence of peroxide gives….[NEET UG 2004]
- Assuming the expression for the pressure exerted by the gas on the walls of the container, it can be shown that pressure is...[MHT CET 2016]
- Which among the following is the strongest acid?...[TS EAMCET 2017]
- Isopropyl alcohol on oxidation forms..
- A vector is not changed if..
- Which of the following arrangements does not represent the correct order of the property stated against it?...[JEE Main 2013]
Sample Questions
Ques: What is osmolarity and its formula? (1 mark)
Ans: Osmolarity is the concentration expressed as osmoles per liter of the solution. Osmolarity is given by the formula= No. of osmoles (osmol) / Volume of solution (in L).
Ques: What are the types of osmotic solutions? (3 marks)
Ans: There are three types of osmotic solutions:
- Isotonic solution: If there is the same concentration of solute both inside and outside the cell, it is an isotonic solution.
- Hypotonic solution: A solution that has a higher solute concentration than the outside solution is called a hypotonic solution.
- Hypertonic solution: If the solute concentration is higher on the outside of the solution, it is called a hypertonic solution.
Ques: What is osmosis and what are the types of osmosis? (3 marks)
Ans: Osmosis is the movement of solute from a higher concentration to a lower concentration across a selectively permeable membrane. It does not require energy. There are two types of osmosis:
Exosmosis: It happens in a hypertonic solution. The solvent will move outside the cell and the cell will undergo plasmolysis.
Endosmosis: It occurs in a hypotonic solution. The solvent will move inside the cell and the cells will undergo deplasmolysis.
Ques: What is a solute? (3 marks)
Ans: The substance that is dissolved in a liquid is called a solute. The liquid in which a solute is dissolved is called a solvent. For example: In a salt solution, the salt that is added is a solute and the water in which it is dissolved is the solvent. If we talk about air, then the gases that are present in the air are considered as a solvent and the water vapor is the solute. This is because the concentration of the gases is present in much more concentration than the water vapors. Ater is considered a universal solvent.
Ques: Calculate the osmolarity of 0.2 M of Na2SO4. (2 marks)
Ans: The molarity is given as M = 0.2.
The formula for osmolarity can be written as, Osmolarity= molarity * n
Where n is the number of ions in which the compound will be dissociated.
Na2SO4., will be dissosiated in 2Na+ and 1 SO42-. Therefore, the value of n=3.
Substituting all the values, osmolarity= 0.2 x 3 = 0.6 OsM
Ques: What is osmotic pressure? (3 marks)
Ans: The pressure that is needed to stop the process of osmosis, is called osmotic pressure. It stops the waters from undergoing diffusion through a semi-permeable membrane. The water will travel from a higher concentration to a lower concentration until the concentration on either side becomes equal. The formula for osmotic pressure is given by
Osmotic pressure= M*R*T
Here, M = Molar concentration
R = Constant
T= Temperature
Ques: What is the difference between osmosis and diffusion? ( 5 marks)
Ans:
| Osmosis | Diffusion |
|---|---|
| The process of osmosis is limited to a liquid medium. | It can occur in all three mediums: solid, liquid, and gas |
| Only the solvent molecule will diffuse | Both solute and solvent can be diffused |
| It requires a semipermeable membrane | It does not require a semi-permeable membrane |
| Require water for the movement | Do not require water for the movement of particles |
| The flow of particles occurs only in one direction | The flow of particles is in all direction |
| Osmosis depends on the number of solute particles | Diffusion depends on the presence of other particles |
For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates
Check-Out:
Comments