Question

What are isotonic solutions?

Hint:

Isotonic = equal osmotic pressure. Example: Medical saline (0.9% NaCl) and blood plasma.

Answer 1

Step 1: Definition.
Two or more solutions having the same osmotic pressure at a given temperature are called isotonic solutions.
Step 2: Explanation.
When two isotonic solutions are separated by a semipermeable membrane, there is no net movement of solvent molecules across the membrane, because both have equal osmotic pressure.
Step 3: Example.
- 0.9% NaCl solution (saline) is isotonic with human blood and tears.
Step 4: Relation.
Osmotic pressure ($\pi$) = $CRT$, where $C$ = concentration, $R$ = gas constant, and $T$ = temperature. For isotonic solutions, $\pi_1 = \pi_2$.