Question

Osmotic pressure of pure water is
(a) Zero atm
(b) 1 atm
(c) 10 atm
(d) 100 atm

Answer 1

Hint: Osmotic pressure is the maximum hydrostatic pressure that a solution could develop when separated from its pure solvent by a selectively permeable membrane. Osmotic pressure is not the physical pressure instead, it is the potential pressure which gets developed in the solution when separated from pure water. It also prevents dilution of solution.

Complete answer
Osmotic pressure of pure water is zero atm. There is no pressure present over the system. In addition to solutes, Osmotic pressure will increase to its maximum.
Let us consider the two solutions. Solution A which contains pure water and Solution B which contains sugar solution. Selectively permeable membrane separates the two solutions. Water molecules will start to diffuse from both the sides, but as more water molecules are striking the membrane from side A as compared to side B. Thus, water will move more rapidly from A to B than from B to A. As a result liquid will rise in chamber B and fall correspondingly in. chamber A. The higher the concentration of sugar solution, the higher will be the rise in liquid B. However, it is possible to keep the level of liquids equal in A and B by applying an external pressure to piston on side B. This pressure is itself called the Osmotic pressure which is required to resist the osmotic flow from solution A to solution B.
Osmotic pressure is directly proportional to the number of solute particles in a given amount of solvent. More is the number of solute particles in a solution, more would be its osmotic pressure. Therefore, Pure water has its Osmotic pressure always zero.

So, the correct answer is ‘Zero atm’.

Note:
Osmotic pressure is the function of solute concentration. The more the solute concentration, greater will be it’s pressure required to prevent water diffusing in.
Both solutions are separated by a selectively permeable membrane. This membrane allows some molecules and ions to enter readily, while allowing others more slowly and does not allow certain molecules at all.
Osmotic pressure is measured by an Osmometer.