Question

Identify the correct statement:

• A. 0.1 M NaCl and 0.1 M glucose solution are isotonic.
• B. 0.1 M NaCl and 0.3 M glucose solution are isotonic.
• C. The boiling point of 0.1 m aqueous urea solution is less than 0.1 m aqueous KCl solution.
• D. The freezing point of 0.1 m glucose solution is less than 0.1 m KCl solution.

Answer 1

Answer: (C)

$\pi =i\times CRT{\pi }_{\text{glucose }}=1\times 0.1\times RT=0.1RT$ ${\pi }_{NaCl}=2\times 0.1RT=0.2RT$ ${\pi }_{NaCl}\ne {\pi }_{\text{glucose }}$
${\pi }_{NaCl}\ne {\pi }_{glucose}$
$\pi =$ osmotic pressurei $=$ van't hoff factor $C=$ Concentration
The boiling point of 0.1 M urea solution is less than that of 0.1 M KCl solution. Because elevation of boiling point is directly proportional to the number of species present in the solution.
KCl is a strong electrolyte(gives 2 ions in aqueous solution)while urea is a non electrolyte(doesn't ionize). Thus, more ions are present in the KCl solution
$\Delta T_{b(KCl)}=2\times 0.1K_f;\Delta T_{b(\text{ urea })}=0.1K_f$
Hence, $\Delta T_{b\text{ (urea) }}<\Delta T_{b(KCl)}$