Question

The molecular, mass of $\text{NaCl}$ as determined by osmotic pressure measurement is:

• A. 58.5
• B. less than 58.5
• C. more than 58.5
• D. unpredicitable

Answer 1

Answer: (B)

$\text{NaCl}$ is an ionic compound. It dissociates into ions in solution. As the osmotic pressure is a colligative property, hence observed osmotic pressure is always greater than the expected. Therefore, molecular weight is always obtained less than 58.5 (mol. wt. of $\text{NaCl}$ ), as: $PV=\frac{W}{M}.ST$