Is 0.3 NaCl an isotonic solution?

To determine if a solution is isotonic, we need to compare its osmotic pressure to that of a reference solution, typically a 0.9% (0.15 M) NaCl solution. Isotonic solutions have the same osmotic pressure as the reference solution, meaning they do not cause net movement of water into or out of cells.

Using the formula for osmotic pressure, π = MRT, where M is the molar concentration, R is the ideal gas constant (0.08206 L·atm/mol·K), and T is the absolute temperature in Kelvin:

For 0.3 M NaCl solution:

π(NaCl) = 0.3 mol/L * 0.08206 L·atm/mol·K * 298 K ≈ 7.6 atm

For 0.15 M NaCl reference solution:

π(reference) = 0.15 mol/L * 0.08206 L·atm/mol·K * 298 K ≈ 3.8 atm

Comparing the osmotic pressures:

0.3 M NaCl solution: 7.6 atm

0.15 M NaCl reference: 3.8 atm

Since the osmotic pressure of the 0.3 M NaCl solution (7.6 atm) is different from that of the reference solution (3.8 atm), this means that it is not isotonic to the reference solution. The 0.3 M NaCl solution has a higher osmotic pressure, which could lead to water movement out of cells placed in this solution.

Therefore, 0.3 M NaCl is not an isotonic solution.