Question

Which aqueous solution has the lowest boiling point?

Answer 1

Answer : The correct option is, (a) 1.25 M $C_6H_{12}O_6$

Explanation :

Formula used for Elevation in boiling point :

$\Delta T_b=i\times k_b\times m$

where,

$\DeltaT_b$ = change in boiling point

$k_b$ = boiling point constant

m = molality

i = Van't Hoff factor

As per question, we conclude that the molality of the given solution are same. So, the boiling point depends only on the Van't Hoff factor.

Now we have to calculate the Van't Hoff factor for the given solutions.

(a) $C_6H_{12}O_6$ is a non-electrolyte solute that means they retain their molecularity, an not undergo association or dissociation.

So, Van't Hoff factor = 1

(b) The dissociation of $KNO_3$ will be,

$KNO_3\rightarrow K^++NO_3^-$

So, Van't Hoff factor = Number of solute particles = 1 + 1 = 2

(C) The dissociation of $KNO_3$ will be,

$AlCl_3\rightarrow Al^[3+}+3Cl^-$

So, Van't Hoff factor = Number of solute particles = 1 + 2 = 3

The boiling point depends only on the Van't Hoff factor.That means lower the Van't Hoff factor, lower will be the boiling point and vice-versa.

Hence, the correct option is, (a) 1.25 M $C_6H_{12}O_6$