Chem_215_Lect_38_Color - Freezing Point Depression and...

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1 Freezing Point Depression and Boiling Point Elevation The vapor pressure of a volatile solvent decreases upon addition of a nonvolatile solute. This leads to an increase in its boiling point Δ T b . The freezing point is lowered by Δ T f Pure water NaCl sol’n 25 o C
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2 Freezing Point Depression Recall that freezing point corresponds to the temperature at which solid is in equilibrium with the liquid: k melt k freezing Solid Liquid
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3 Freezing Point Depression and Boiling Point Elevation The vapor pressure of a volatile solvent decreases upon addition of a nonvolatile solute. This leads to an increase in its boiling point Δ T b . The freezing point is lowered by Δ T f Δ T f = - K f x m Boiling point elevation constant Molality (mol/kg) Freezing point depression constant Molality (mol/kg) Δ T b = K b x m
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