Discussion Forum



1)

The correct relation between elevation of boiling point and molar mass of solute is 


A) $m_{2}=\frac{k_{b}.w_{2}}{\triangle T_{b}.w_{1}}$

B) $m_{2}=\frac{k_{b}.w_{1}}{\triangle T_{b}.w_{2}}$

C) $M_{2}=\frac{\triangle T_{b}.k_{b}}{w_{1}..w_{2}}$

D) $M_{2}=\frac{\triangle T_{b}.w_{1}}{k_{b}.w_{2}}$

Answer:

Option A

Explanation:

 For dilute solutions, the elevation  is boiling point is directly proportional to the molal concentration  pf the solute in solution (m) 

 Thus,  $\triangle T_{b}\propto m$

 $\triangle T_{b}= k_{b}m$

 where, kb is molal boiling point elevation constant

As, molality (m)= Moles of solute(n2) / Mass of solvent (W1)(in kg)

 Moles of solute $(n_{2})= \frac{W_{2}}{M_{2}}$

$\therefore$   $\triangle T_{b}= \frac{k_{b}\times W_{2}}{M_{2}\times W_{1}}$

$\Rightarrow$    $ M_{2}= \frac{k_{b}. W_{2}}{\triangle T_{b}. W_{1}}$