Question

What will be the direction of the movement of water when two solutions with ${{\text{ }\\!\\!\psi\\!\\!\text{ }}_{\text{ }\\!\\!\omega\\!\\!\text{ }}}=0.2\text{MPa}$ and ${{\text{ }\\!\\!\psi\\!\\!\text{ }}_{\text{ }\\!\\!\omega\\!\\!\text{ }}}=0.2\text{MPa}$ are separated by a selectively permeable membrane?

Answer 1

The movement of water between two solutions separated by a selectively permeable membrane is dependent on their water potential. The water potential is denoted by ${{\text{ }\\!\\!\psi\\!\\!\text{ }}_{\text{ }\\!\\!\omega\\!\\!\text{ }}}$.

Complete answer:
Water potential is the potential energy of the water which helps in its movement and is measured in Pascals. The water molecules possess kinetic energy and thus are always in random motion. This kinetic energy is directly proportional to the concentration of the water. So, pure water has the maximum kinetic energy and thus, maximum water potential.

If two solutions of water are in contact with each other through a semi-permeable or selectively permeable membrane, the water will move in a way to form an equilibrium. The movement of water to form equilibrium is always from the system having higher energy to the system having lower energy. In other words, the water will move from the system having higher water potential to the system having lower water potential till the equilibrium is reached. This movement of water across a membrane to form equilibrium is known as diffusion. In this case, the water will move from the solution with water potential 0.2 MPa to the solution with water potential 0.1 MPa.

Note: Water potential is dependent upon the solute potential and pressure potential. If any solute is added to the water, then the concentration of water decreases and so, the water potential is decreased. The degree by which the water potential is decreased is known as solute potential. So, all the solutions have lesser potential than that of pure water.