Question

The water potential and osmotic potential of pure water are
A. 100 and 0
B. 0 and 0
C. 100 and 200
D. 0 and 100

Answer 1

Osmosis is the net diffusion of water molecules from a dilute solution to the concentrated solution when the two are separated by means of a semi-permeable membrane. If the solution is separated from its pure solvent, the molecules of the solvent move from pure solvent to the solution.

Complete answer: A pure water (or solvent) has maximum free energy, diffusion pressure, and chemical potential ( in case of water; water potential). When some soluble substance is dissolved into it, the free energy of water decreases.
-The osmotic pressure of a solution is equivalent to the pressure which must be exerted upon it to prevent the flow of solvent into it across a semipermeable membrane. In other words, the maximum amount of pressure that can be developed in a solution separated from pure water by a semipermeable membrane is termed osmotic pressure. It is usually measured in Pascal (Pa).
-Water potential: It is the water molecules that possess kinetic energy. In liquid and gaseous forms they are in random states that are both rapid and constant. The greater the concentration of water in a system the greater is this kinetic energy or water potential. Hence it is observed that pure water will have a greater water potential. The water potential of pure water at standard temperature, which is not under any pressure, is taken to be zero.
The osmotic potential and water potential of pure water is zero as the pure water does not have any dissolved salts.
So, the correct answer is option B, i.e., 0 and 0.

Note: If some solute is dissolved in pure water, the solution has fewer free water, and the concentration of water decreases, reducing its water potential. Hence, all solutions have lower water potential than pure water, the magnitude of its lowering due to dissolution of salt is called solute potential.