Osmosis & Osmotic pressure

Osmosis:

⇒ The movement of solvent molecules through a semi-permeable membrane (kept between a pure solvent and its solution) from pure solvent to solution is osmosis.

⇒ The movement of solvent molecules continues till equilibrium is reached.

⇒ Solvent molecules move from lower concentration solution to higher concentration solution.

 

Osmotic pressure:

⇒ The excess pressure exerted on the solution side to stop the movement of solvent molecules into the solution.

⇒ Depends on concentration of solution

At a given temperature,

π α C

π = CRT

π = Osmotic Pressure

C = molarity

R = gas constant

T = Temperature

Isotonic solutions: Two solutions having same osmotic pressure at a given temperature.

Hypertonic solution: Any solution with a higher salt concentration than normal body cells so that the water is drawn out of the cells by osmosis. Hypertonic solutions have higher osmotic pressure.

Hypotonic solution: Any solution with a lower concentration than normal body cells so that water flows into the cells by osmosis. Hypotonic solutions have lower osmotic pressure.

Reverse Osmosis:

⇒ When pressure greater than osmotic pressure is applied on the solution, the solvent molecules move from solution to pure solvent. This is reverse osmosis

⇒ Used in sea water purification

⇒ Reverse osmotic pressure > osmotic pressure.

 

Determination of molar mass: We can determine the molecular weights of the solute using colligative properties.

The molecular weight Relates with magnitude of a colligative properties as.

Molecular Mass α 1/ Magnitude of colligative property

1. From vapour pressure:

Where, w_A = mass of solvent

M_A = Molar mass of solvent

W_B = mass of solute

M_B = Molar mass of solute

2. From boiling point:

M₂ = molar mass of solute

W₂= mass of solute

K_b = Molal elevation constant

∆T_b = elevation in boiling point

3. From freezing point:

M₂ = molar mass of solute

W₂= mass of solute

K_f = Molal depression constant

∆T_f = depression in freezing point

4. From osmotic pressure:

M₂ = molar mass of solute

R = gas constant

T = temperature

π = osmotic pressure

V = Volume of the solution in liters.