Unit 3 (IMFs & Properties): How Chemists Understand, Represent, Separate, and Predict Solutions

Mixture

A physical combination of substances in which each component retains its own chemical identity; properties depend on how particles are combined and interact.

Homogeneous Mixture

A mixture with uniform composition throughout; any small sample has the same proportions of components.

Heterogeneous Mixture

A mixture with non-uniform composition; different regions contain different proportions of components.

Solution

A homogeneous mixture at the particle level in which solute particles are evenly dispersed among solvent particles so regions of different composition cannot be distinguished.

Solute

The substance being dissolved in a solution.

Solvent

The substance that does the dissolving and forms the continuous phase of a solution (often present in greater amount).

Suspension

A heterogeneous mixture with large particles that settle out over time; often separable by filtration.

Colloid

A heterogeneous mixture with intermediate-sized particles that do not settle out easily; not a “true solution.”

Tyndall Effect

Light scattering by particles in a colloid, used as an observable test to distinguish colloids from true solutions.

Intermolecular Forces (IMFs)

Attractive forces between particles (e.g., dispersion, dipole-dipole, hydrogen bonding) that strongly influence dissolving and solution behavior.

Like Dissolves Like

Guideline that substances with similar polarity and IMF types tend to be soluble/miscible because new solute–solvent attractions can compensate for attractions broken during dissolving.

Dissociation vs. Ionization

Dissociation: separation of pre-existing ions from an ionic solid in solution (e.g., NaCl → Na⁺ + Cl⁻). Ionization: formation of ions from neutral molecules in water (common for weak acids/bases).

Hydration

Solvation specifically by water: water molecules surround dissolved particles/ions; in ion hydration, water’s O end points toward cations and H ends toward anions (ion–dipole attraction).

Electrolyte

A substance that produces ions in solution, allowing the solution to conduct electricity due to mobile charged particles.

Strong vs. Weak Electrolytes

Strong electrolytes produce many ions in solution (e.g., strong acids, many soluble ionic compounds). Weak electrolytes partially ionize, producing fewer ions and weaker conductivity.

Nonelectrolyte

A substance that dissolves as neutral molecules (does not form ions) and therefore conducts electricity poorly (e.g., sucrose in water).

Molarity (M)

A concentration unit defined as moles of solute per liter of solution: M = n/V (with V in liters).

Chromatography

A family of separation techniques that separates mixture components based on different attractions to a stationary phase and a mobile phase (IMFs in action).

Stationary Phase vs. Mobile Phase

Stationary phase: the fixed surface (often polar paper/cellulose or silica). Mobile phase: the solvent that moves through/along the stationary phase and carries solutes by repeated dissolving/adsorbing.

Retention Factor (Rf)

In TLC/paper chromatography, the ratio Rf = dsolute/dsolvent (distance spot moved divided by distance solvent front moved); unitless and condition-dependent.

Solubility

The maximum amount of solute that can dissolve in a given amount of solvent under specified conditions (typically temperature; pressure also matters for gases).

Saturated Solution

A solution containing the maximum dissolved solute at equilibrium; dissolving and crystallizing occur at equal rates (dynamic equilibrium).

Unsaturated Solution

A solution containing less than the maximum amount of solute at that temperature; additional solute can still dissolve.

Supersaturated Solution

A metastable solution containing more dissolved solute than the equilibrium maximum; easily crystallizes if disturbed or seeded.

Henry’s Law

For gases dissolving in liquids at constant temperature, solubility is proportional to the gas’s partial pressure above the solution: S = k_H P.