Question

Describe various laws of osmotic pressure.

Answer 1

1. Boyle-van’t Hoff law: According to this law, the osmotic pressure of a dilute solution is directly proportional to its concentration provided temperature remains constant.
   Let π be the osmotic pressure and C the concentration of a dilute solution. According to this law,
   π ∝ C (at constant temperature)    ...(i)
   If the concentration of solution is expressed in moles per litre and V is the volume containing one mole of the solute, C = 1/V. Therefore, relation (i) can be written as
   `pi prop 1/V` (at constant temperature)    ...(ii)
   This relationship is similar to Boyle’s law for gases and is known as Boyle-van’t Hoff law.
2. Charles’-van’t Hoff law: According to this law, the osmotic pressure of a dilute solution is directly proportional to the absolute temperature if the concentration of the solution is kept constant.
   Mathematically,
   π ∝ T (at constant concentration)
   This relationship is similar to Charles’ law for gases and is known as the Charles’-van’t Hoff law.
3. Avogadro-van’t Hoff law: According to this law, equal volumes of solutions contain equal numbers of moles (molecules) of solute provided their osmotic pressure and temperature are the same.
   This statement is similar to Avogadro’s law for gases and is known as the Avogadro-van’t Hoff law.