Solids in Solution and Colligative Properties: Screencasts

Explains the meanings of saturated and supersaturated solutions and discusses the temperature dependent of solubility.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Uses a pressure-temperature phase diagram to explain why adding a solid solute to a solvent change boiling and freezing points.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Optional screencast: Derive Equation for Boiling Point Elevation

Important Equations:

Solute lowers the saturation pressure of solvent.

\[P_{solvent} = (1-x)P_{solvent}^{sat}\]

where \(P_{solvent}\) = the pressure of solvent with dissolved solute,
\(P_{solvent}^{sat}\)= the pure-component solvent saturation pressure, and
\(x\) = the mole fraction of the solute.

Clausius-Clapeyron equation: \(\mathrm{ln}(P^{sat}) = -\frac{\Delta H_{vap}}{RT} +B\)

where \(P_{sat}\) = saturation pressure at temperature T,

\( \Delta H_{vap}\) = heat of vaporization (J/mol),
\(R\) = ideal gas constant (J/(mol K), and,
\(B\) = a constant, which is different for each molecule

Dilute Solutions

\[\Delta T_{boil} = \frac{RT_{boil}^2x}{\Delta H_{vap}}\]

where \(\Delta T_{boil}\) = increase in boiling point temperature of solvent with dissolved solute (K)
\(R\) = ideal gas constant (J/(mol K)),
\(T_{boil}\) = boiling point temperature of pure solvent (K), and
\(\Delta H_{vap}\)= heat of vaporization of pure solvent (J/mol).

\[\Delta T_{m} = \frac{RT^2_{m}x}{\Delta H_{m}}\]

where \(\Delta T_{m}\) = decrease in boiling point temperature of solvent with dissolved solute (K)
\(T_{m}\) = freezing point temperature of pure solvent (K), and
\(\Delta H_{m}\)= heat of fusion (J/mol).
When x is small, ln(1-x) is approximately equal to -x.