Question

The of slope for the graph between $(T_b-T_b^{\circ })$ and molality is equal to :
where ,
$T_b\text{indicates boiling point of solution}$
$T_b^{\circ }\text{indicates boiling point of pure solvent}$

• A. $\text{Number of moles of solute}$
• B. $\text{Number of moles of solvent}$
• C. $\text{Vapour pressure of pure solvent}$
• D. $\text{Boiling point elevation constant}\left(K_b\right)$

Answer 1

The correct option is D $\text{Boiling point elevation constant}\left(K_b\right)$

$\Delta T_b=T_b-T_b^{\circ }$
Elevation in Boiling Point
Elevation of BP is only dependent on the solute concentration and not its nature.
The slope of the graph between $(T_b-T_b^{\circ })$ v/s molality gives $K_b$ i.e. Boiling Point Elevation Constant or Molal Elevation Constant
It is also known as ebullioscopic constant.
From experimental observations:
$\Delta T_b=K_b\times m$
Here m is molality.