Chapter 13, Problem 13.45QP

Interpretation Introduction

Interpretation:

Explain Freezing point depression and osmotic pressure measurements used to determine the molar mass of a compound but boiling point elevation and vapor pressure lowering not used to be described.

Concept introduction:

Boiling point is the temperature at which liquid turns into a gas. Example: boiling point of water is $\text{100}{}^{\text{o}}\text{C}$. That is water changes from liquid phase to gas phase.

${\text{ΔT}}_{\text{b}}{\text{= T}}_{\text{b}}{\text{- T}}_{\text{b}}^{\text{°}}$

Where,

${\text{ΔT}}_{\text{b}}-$ Change in boiling point

${\text{T}}_{\text{b}}-$ Boiling point of the solution

${\text{T}}_{\text{b}}^{\text{°}}-$ Boiling point of pure solvent

Boiling point elevation $({\text{ΔT}}_{\text{b}})$ is depicted as follows,

${\text{ΔT}}_{\text{b}}{\text{= K}}_{\text{b}}\text{m}$

Where,

${\text{ΔT}}_{\text{b}}-$ Change in boiling point

${\text{K}}_{\text{b}}-$ Molal boiling point constant

$m-$ Molality of the solution

Freezing point is the temperature at which liquid turns into solid.

Freezing point depression ${\text{(ΔT}}_{\text{f}}\text{)}$ is depicted as follows,

${\text{ΔT}}_{\text{f}}{\text{= K}}_{\text{f}}\text{m}$

Where,

${\text{ΔT}}_{\text{f}}-$ Change in freezing point

${\text{K}}_{\text{f}}-$ Molal freezing point constant

$m-$ Molality of the solution

Osmotic pressure is the pressure that is needed to stop osmosis. Osmotic pressure of the solution is directly proportional to the concentration of the solution.

Osmotic pressure $\text{(π) = MRT}$

Where,

$M–$ Molarity of the solution $\left(\text{mol/L}\right)$

$R-$ Ideal gas constant $\left(0.08206{\text{L atm mol}}^{\text{-1}}{\text{K}}^{\text{-1}}\right)$

$T-$ Temperature in Kelvin