Question

What are isotonic solutions?

Answer 1

Hint: Think about the meanings of both the parts ‘iso-’ and ‘-tonic’. ‘Iso-’ is derived from the Greek word that means equal. ‘-tonic’ is derived from tonicity. Try to relate these meanings to the properties of any solution and think about what it means for two solutions to have equal tonicity.

Complete answer:
The word ‘isotonic’ refers to the tonicity that is present between two separated areas or solutions. Tonicity essentially means the relative concentration of two solutions and is a measure of the total osmotic gradient that may be present between them.
Two solutions are said to be isotonic if the concentration gradient between them is effectively zero. There should be no net flow of water from one side of the semipermeable membrane to the other. The osmotic pressure that is exerted by both the fluids on the semipermeable membrane should be the same.
There will be some movement of water from one side to another due to fluctuations in external conditions but equilibrium will soon be established in any two isotonic solutions.

Additional Information A general overview of the osmotic concentrations of two solutions can be received if they are labeled as either hypertonic, hypotonic, or isotonic. In a hypertonic solution, the solute concentration is more than that of the solution across the semipermeable membrane. Water will flow into the compartment that contains the hypertonic solution. The other solution in this same example will be hypotonic with respect to the other and water will flow out of it.

Note: Please do not assume that if two solutions are isotonic then they must have the same volume. The two sides of the semipermeable membrane may have vastly different volumes of the solution but no net flow will be seen since the osmotic concentration is the same.