Question

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

• A. $\text{Number of moles of solute}$
• B. $\text{Molal Depression Constant}$
• C. $\text{Vapour pressure of pure solvent}$
• D. $\text{Molal Elevation Constant}$

Answer 1

The correct option is B $\text{Molal Depression Constant}$

Depression of freezing point $(\Delta T_f=(T_f^{\circ }-T_f\left)\right)$ for dilute solution (ideal solution) is directly proportional to molality (m) of the solution.
$\Delta T_f=K_f\times m$
$K_f$ is is Freezing Point Depression Constant, Cryoscopic Constant or Molal Depression Constant.
Depression in freezing point is a colligative property since depression in F.P. is only dependent on solute concentration and not its nature.