Osmotic Pressure Vs Osmotic Potential: What Is The Difference?


What Is Osmotic Potential?

Osmosis takes place across water potential gradient i.e water moves from a region of high water potential to a region of low water potential. Water potential is the measure of concentration of free water molecules (the ones that are free to move) in other words, the potential energy.

Water potential of pure water is zero (kPa) and that of a given sample, containing solutes, is a negative number. When solutes are present in water, water molecules tend to react with them or surround solute molecules and hence are less free to move, thus the negative potential (thus the negative potential).This also means that the more solute concentration, the lesser would be the tendency of water molecules to diffuse.

Osmotic potential also referred to as solute potential, is a measure of water potential for movement from a region of lower solute concentration to a region of higher solute concentration. Osmotic potential decreases with an increase in solute concentration (since water molecules will be free to move due to more solute molecules).

What You Need To Know About Osmotic Potential

  • Osmotic potential is the potential of water molecules to move from a hypotonic solution (more water, less solutes) to a hypertonic solution (less water, more solute) across a semi-permeable membrane.
  •  Osmotic potential can also be defined as the free energy that enables water molecules to move across a semi permeable membrane due to presence of solute particles.
  • Osmotic potential develops in a closed or open system.
  • The value of osmotic potential is negative.
  • Difference in osmotic potential will cause water molecules to move from a hypotonic solution to a hypertonic solution.
  • In application, when two solutions are isotonic, the osmotic potentials will be equal and there will be no net movement of water molecules.

What Is Osmotic Pressure?

Osmosis entails the flow of water/solvent molecules from a region of low solute concentration to a region of high solute concentration across a semi-permeable membrane until equilibrium is established. Therefore, in order to counter osmotic flow, some pressure must be applied to the solution so as to prevent pure solvent from going through the semi-permeable membrane separating the two liquids; this is what is referred to as osmotic pressure.

Osmotic pressure is still a useful concept especially when the differential movement of water is related to other hydraulic phenomena such as arteriole pressure (in the physiology of kidneys) and to the use of reverse osmosis for desalinating sea water using hydraulic pressure to create distilled water from a saline solution through a selectively permeable membrane.

What You Need To Know About Osmotic Pressure

  • Osmotic pressure is the hydrostatic pressure which develops in an osmotic system to prevent the inward flow of water across the semi-permeable membrane. It can also be defined as the pressure required to stop/counter osmosis.
  • Osmotic pressure develops in a closed system.
  • The value of osmotic pressure is positive.
  • Osmotic pressure can only exist when the concentration of particles in the two solutions are unequal.
  • In application, osmotic pressure measurement may be used for determination of molecular weights.

Also Read: Difference Between Osmosis And Diffusion