Question

$8\%$ aqueous solution of urea (by mass of solvent) has elevation in boiling point $x_1.20\%$ aqueous solution of glucose (by mass of solvent) has elevation in boiling point $x_2$. If these two solutions are mixed then, elevation in boiling point is $x_3$. Then,

• A. $x_1+x_2=x_3$
• B. $3x_1+x_2=x_3$
• C. $x_1<x_2<x_3$
• D. $x_1=x_2=x_3$

Answer 1

Answer: (D)

$6\%$ urea solution, $\Delta T_b=\frac{1000K_b{w}_1}{m_1{w}_2}$

$\Delta T_b($ urea $)=x_1=\frac{1000\times K_b\times 8}{60\times 100}=K_b$

$\Delta T_b($ glucose $)=x_2=\frac{1000\times K_b\times 20}{60\times 100}=K_b$

$\Delta T_b$ (mixture) $=\frac{1000(\text{ total moles of solute })K_b}{\text{ Total mass of solvent }}$

$=\frac{1000\times K_b\times 25}{200}$

$x_3=K_b$

Thus, $x_1=x_2=x_3$