Question

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

• A. $x_1+x_2=2x_3$
• B. $3x_1+x_2=x_3$
• C. $x_1<x_2<x_3$
• D. $x_1=x_2=x_3$

Answer 1

The correct option is A $x_1+x_2=2x_3$

Since the van ‘t Hoff factor for both urea and glucose are 1, and elevation in boiling point is a colligative property, it is only dependent on the concentration of solute particles.
Let’s take 1 L of both the solutions and mix it .The concentration of both - urea and glucose will reduce to half of their initial value that is
$\frac{x_1}{2}+\frac{x_2}{2}=x_3$
$\therefore x_1+x_2=2x_3$