Solutions and Colligative Properties — Lecture Notes

Vocabulary flashcards covering key terms and concepts from solution chemistry, including colligative properties, Raoult's law, and osmotic terminology.

Boiling point elevation

The increase in a solvent's boiling point when a nonvolatile solute is dissolved; ΔTb = i Kb m, where i is the van't Hoff factor and m is molality.

Freezing point depression

The lowering of a solvent's freezing point when a nonvolatile solute is dissolved; ΔTf = i Kf m, with i as the van't Hoff factor and m as molality.

Cryoscopic constant (Kf)

The proportionality constant for freezing point depression for a given solvent; example for water is Kf = 1.86 °C·kg/mol.

Boiling point elevation constant (Kb)

The proportionality constant for boiling point elevation for a solvent; example for water is Kb = 0.512 °C·kg/mol.

Van't Hoff factor (i)

The number of particles produced in solution per formula unit of solute; scales colligative properties (e.g., i ≈ 1 for nonelectrolytes, higher for electrolytes that dissociate).

Molality (m)

Moles of solute per kilogram of solvent; used in equations for boiling/freezing point changes and other colligative properties.

Raoult's Law

In solutions with a nonvolatile solute, the vapor pressure is Psoln = Xsolvent · P°solvent, where Xsolvent is the mole fraction of the solvent.

Mole fraction (X)

The fraction of moles of a component relative to the total moles in the mixture; X_solvent is used in Raoult's Law.

Nonvolatile solute

A solute that has negligible vapor pressure and thus lowers the solvent's vapor pressure in a solution.

Vapor pressure

The pressure exerted by the vapor of a liquid in equilibrium with its liquid; decreases when a nonvolatile solute is present.

Osmosis

The flow of solvent through a semipermeable membrane from the side with lower solute concentration to the side with higher solute concentration.

Hypotonic

A solution with lower solute concentration than the comparison side; water tends to move into the higher-concentration side (cell swelling are context-dependent).

Hypertonic

A solution with higher solute concentration than the comparison side; water tends to move out of the cell.

Isotonic

Two solutions with the same solute concentration; no net flow of solvent across the membrane.

Percent by volume

A concentration expressed as the volume of solute per volume of solution (volume percent); often converted to molarity via density and mass calculations.

Density

Mass per unit volume used to convert volumes to masses (e.g., g/mL); essential for turning volume percentages into moles.

Molarity vs Molality

Molarity (M) is moles of solute per liter of solution; Molality (m) is moles of solute per kilogram of solvent; colligative properties are typically expressed with molality.