Solutions used for intravenous injections must be isotonic, that is, exert an osmotic pressure of 6.9 atm. An isotonic saline solution uses sodium chloride as the solute to achieve isotonic conditions. Use this value for the osmotic pressure to estimate the % NaCl by mass in an isotonic saline solution at 37°C (assume the solution has a density of 1.0 g/mL).

Question

Quizplus · Accepted Answer

To find the % NaCl by mass in an isotonic saline solution, we can use the formula for osmotic pressure: $\Pi = iMRT$, where $\Pi$ is the osmotic pressure (6.9 atm), $i$ is the van't Hoff factor for NaCl (which dissociates into 2 ions, Na+ and Cl-, so $i = 2$), $M$ is the molarity of the solution, $R$ is the ideal gas constant (0.0821 L·atm/K·mol), and $T$ is the temperature in Kelvin (310 K for 37°C).Rearranging the formula to solve for $M$: $M = \frac{\Pi}{iRT}$Substituting the given values: $M = \frac{6.9}{2 \times 0.0821 \times 310} = \frac{6.9}{50.526} \approx 0.1365$ MTo find the mass percent, we need to know the mass of NaCl in 1 L of solution (which is 1000 g due to the density of 1.0 g/mL) and the molar mass of NaCl (58.44 g/mol).Mass of NaCl in 1 L = $0.1365 \text{ mol} \times 58.44 \text{ g/mol} = 7.98 \text{ g}$Mass percent = $\frac{7.98 \text{ g}}{1000 \text{ g}} \times 100\% = 0.798\%$This value is closest to 0.80%, which is option D.

Solutions Used for Intravenous Injections Must Be Isotonic, That Is