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)

$\pi= i \times CRT \pi_{\text {glucose }}=1 \times 0.1 \times RT =0.1 RT$ $\pi_{ NaCl }=2 \times 0.1 RT =0.2 RT$ $\pi_{ NaCl } \neq \pi_{\text {glucose }}$
$\pi _{N a C l}\neq \pi _{g l u cos e}$
$\pi=$ 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 0.1 K _{ f } ; \quad \Delta T _{ b (\text { urea })}=0.1 K _{ f } $
Hence, $\Delta T _{ b \text { (urea) }}<\Delta T _{ b ( KCl )}$