Chemistry of Solutions and Colligative Properties

Vocabulary flashcards covering basic solution terminology, concentration units, solubility principles, gas laws for solutions, and colligative properties.

Solution

A homogeneous mixture of two or more substances.

Solvent

The component of a solution present in the largest amount; does the dissolving.

Solute

The component(s) of a solution present in smaller quantity; what gets dissolved.

Aqueous (aq)

A solution in which water is the solvent.

Miscible

Two liquids that dissolve in each other completely, e.g., ethanol and water.

Immiscible

Two liquids that do NOT dissolve in each other, e.g., oil and water.

Soluble

A solute has high solubility in a given solvent under given conditions.

Insoluble

A solute has low solubility in a given solvent under given conditions.

Unsaturated solution

A solution in which more solute can still be dissolved.

Saturated solution

A solution holding the maximum amount of dissolved solute possible under given conditions.

Supersaturated solution

A solution holding more than the maximum amount of solute normally dissolved; unstable state.

Electrolyte

A substance that dissociates into ions when dissolved in water; its solutions conduct electricity.

Likes Dissolve Likes

The principle that solubility is determined by the type of intermolecular attractive force, not its strength; substances mix when they share similar attractive forces.

Hydrophilic

"Water-loving"; describes polar or ionic groups ($O-H$, $N-H$, $C=O$) that interact favorably with water through hydrogen bonding.

Hydrophobic

"Water-fearing"; describes nonpolar hydrocarbon chains and rings ($C-C$, $C-H$ bonds) that do not interact favorably with water.

Henry's Law

$P_A = k_H C_A$; the partial pressure of a gas above a solution is directly proportional to its concentration dissolved in the solution.

k_H (Henry's Law constant)

A constant specific to a particular solute-solvent pair at a particular temperature, relating partial pressure to dissolved concentration in Henry's Law.

Dalton's Law

$P_A = Y_A P_{\text{Total}}$; used first to find a gas's partial pressure from its percent composition in a gas mixture before applying Henry's Law.

Molarity (M)

$M = \frac{\text{moles solute}}{\text{liters solution}}$; concentration measure that changes with temperature because solution volume changes with temperature.

Molality (m)

$m = \frac{\text{moles solute}}{\text{kg solvent}}$; concentration measure that does NOT change with temperature because mass is constant.

Mass percent (%m/m)

$\frac{\text{mass solute}}{\text{mass solution}} \times 100$, where mass of solution equals mass of solute plus mass of solvent.

Volume percent (%v/v)

$\frac{\text{volume solute}}{\text{volume solution}} \times 100$; typically used when both solute and solvent are liquids.

Mass by volume percent (%m/v)

$\frac{\text{grams solute}}{\text{mL solution}} \times 100$; commonly used in medicine.

Mole fraction (X_A)

$X_A = \frac{\text{moles of A}}{\text{total moles in the solution}}$; the sum of all mole fractions in a solution must equal 1.

Dilution equation

$C_1 V_1 = C_2 V_2$, valid for any concentration unit as long as $C_1$ and $C_2$ share the same unit, and $V_1$ and $V_2$ share the same unit.

Serial dilution

Diluting a solution, then taking a small aliquot of that diluted solution and diluting it again, repeatable multiple times.

Ionic compound dissociation

Ionic compounds dissociate into ions in the ratio given by the subscripts of the ionic formula, e.g., $MgBr_2$ dissociates into $Mg^{2+}$ and $2 Br^{-}$.

Vapor pressure

The partial pressure of a gas above its own liquid caused by evaporation.

Volatile

Describes a substance with a high tendency to evaporate and therefore a high vapor pressure.

Nonvolatile

Describes a substance that does not evaporate appreciably and therefore has negligible vapor pressure.

Raoult's Law

$P_A = X_A P_A^{*}$, where $P_A$ is the vapor pressure of the liquid in the solution, $P_A^{*}$ is the vapor pressure of the pure liquid, and $X_A$ is the mole fraction of A in the liquid/solution phase.

Ideal solution

A solution in which solute-solvent interactions are similar in strength to solute-solute and solvent-solvent interactions.

Negative deviation from Raoult's Law

Lower than expected total vapor pressure, observed when solute-solvent interactions are stronger than the interactions in the pure substances.

Positive deviation from Raoult's Law

Higher than expected total vapor pressure, observed when solute-solvent interactions are weaker than the interactions in the pure substances.

Van't Hoff factor (i)

$i = \frac{\text{moles of dissolved particles}}{\text{moles of solute dissolved}}$; equals 1 for nonelectrolytes and the number of ions per formula unit for electrolytes.

Colligative property

A property that depends only on the amount (concentration) of dissolved particles, not on their chemical identity.

Boiling point elevation

Dissolved solutes increase a solution's boiling point because they lower vapor pressure, requiring more heat to raise vapor pressure back up to atmospheric pressure.

Boiling point elevation formula

$\Delta T_b = i \times K_b \times m$, where $\Delta T_b$ is the change in boiling point, $K_b$ is the solvent's boiling point elevation constant, and $m$ is molality.

Freezing point depression

Dissolved solutes decrease a solution's freezing point because they interfere with the solvent's ability to organize into an ordered solid lattice.

Freezing point depression formula

$\Delta T_f = -i \times K_f \times m$, where $\Delta T_f$ is the change in freezing point, $K_f$ is the solvent's freezing point depression constant, and $m$ is molality.

Osmosis

The flow of solvent through a semipermeable membrane from a region of low solute concentration to a region of high solute concentration.

Isotonic solution

A solution with equal osmotic pressure to another solution; no net water flow occurs.

Hypotonic solution

A solution with lower solute concentration than a reference solution; water flows into the cell.

Hypertonic solution

A solution with higher solute concentration than a reference solution; water flows out of the cell.

Osmotic pressure formula

$\pi = i \times R \times T \times M$, where $\pi$ is osmotic pressure, $i$ is the van't Hoff factor, $R$ is the gas constant, $T$ is temperature in Kelvin, and $M$ is molarity.