LearnChemE

#### 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.