Osmosis and Osmotic pressure
- We have often observed that raw mangoes shrink when kept in salt water (brine solution), flowers remain fresh for longer time when kept in water.
- This is due to the fact that small solvent molecules such as water are capable of passing through the pores present in every cell. These pores allows small solvents like water to pass through but hinders the passing of larger molecules. This membrane possessing such pore is known as semipermeable membranes.
- The process of flow of solvents from the pure solvent to the solution through a semipermeable membrane is termed as osmosis.
- This flow of solvents to the solution continues until the stage of equilibrium is reached.
- Application of extra pressure on the solution can terminate the flow of solvents from the pure solvent to the solution. This pressure is called osmotic pressure of the solution. It is a colligative property that depends upon the concentration of the solution and is basically meant to stop the passage of solvent molecules through a semipermeable membrane into the solution.
- Solvent molecules generally flows from lower concentration to higher concentration. This flow of solvent from dilute solution to the concentrated solution through a semipermeable membrane is due to the phenomenon of osmosis.
Calculate the osmotic pressure in Pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL of water at 37°C.
Sol. Volume of water, V= 450 mL = 0.45 L
Temperature, T = (37 + 273) K = 310 K
Number of moles of the polymer, n = 1 / 185000 mol
Osmotic pressure ð (n/V)RT
= 1/185000 mol X 1/0.45L X 8.314 X 103 Pa L K-1mol-1 X 310K
= 30.98 Pa = 31 Pa
