Chapter 13

The Properties of Mixtures: Solutions and Colloids

**alloy**

A mixture with metallic properties that consists of solid phases of two or more pure elements, a solid-solid solution, or distinct intermediate phases.

**amino acid**

An organic compound \[general formula, H2N─CH(R)─COOH\] with at least one carboxyl and one amine group on the same molecule; the monomer unit of a protein.

**boiling point elevation (ΔTb)**

The increase in the boiling point of a solvent caused by the presence of dissolved solute.

**charge density**

The ratio of the charge of an ion to its volume.

**colligative property**

A property of a solution that depends on the number, not the identity, of solute particles. (See also *boiling point elevation, freezing point depression, osmotic pressure,* and *vapor pressure lowering.*)

**colloid**

A heterogeneous mixture in which a dispersed (solute-like) substance is distributed throughout a dispersive (solvent-like) substance.

**desalination**

A process used to remove large amounts of ions from seawater, usually by reverse osmosis.

**dipole–induced dipole force**

The intermolecular attraction between a polar molecule and the oppositely charged pole it induces in a nearby molecule.

**double helix**

The two intertwined polynucleotide strands held together by H bonds that form the structure of DNA (deoxyribonucleic acid).

**entropy (S)**

A thermodynamic quantity related to the number of ways the energy of a system can be dispersed through the motions of its particles.

**fractional distillation**

A physical process involving numerous vaporization-condensation steps used to separate two or more volatile components.

**freezing point depression (ΔTf)**

The lowering of the freezing point of a solvent caused by the presence of dissolved solute particles.

**hard water**

Water that contains large amounts of divalent cations, especially Ca2+ and Mg2+.

**heat of hydration (ΔHhydr)**

(also *enthalpy of hydration*) The enthalpy change occurring when 1 mol of a gaseous species (often an ion) is hydrated. The sum of the enthalpies from separating water molecules and mixing the gaseous species with them; designated (delta H of hydration) at the standard state.

**heat of solution (ΔHsoln)**

(also *enthalpy of solution*) The enthalpy change occurring when a solution forms from solute and solvent. The sum of the enthalpies from separating solute and solvent substances and mixing them; designated ( Delta H of solution) at the standard state.

**Henry’s law**

A law stating that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid: *S* gas = *k* H × *P* gas.

**hydration**

Solvation in water.

**hydration shell**

The oriented cluster of water molecules that surrounds an ion in aqueous solution.

**ideal solution**

A solution that follows Raoult’s law at any concentration.

**immiscible**

Insoluble; usually applied to liquids that do not dissolve in each other.

**ion exchange**

A process of softening water by exchanging one type of ion (usually Ca2+) for another (usually Na+) by binding the ions on a specially designed resin.

**ionic atmosphere**

A cluster of ions of net opposite charge surrounding a given ion in solution.

**ion–induced dipole force**

The attractive force between an ion and the dipole it induces in the electron cloud of a nearby nonpolar molecule.

**like-dissolves-like rule**

An empirical observation stating that substances having similar kinds of intermolecular forces dissolve in each other.

**lipid bilayer**

An extended, sheetlike double layer of phospholipid molecules that forms in water and has the charged heads of the molecules on the surfaces of the bilayer and the nonpolar tails within the interior.

**mass percent [% (w/w)]**

(also *mass %* or *percent by mass*) The fraction by mass expressed as a percentage. A concentration term expressed as the mass of solute dissolved in 100. parts by mass of solution.

**miscible**

Soluble in any proportion.

**molality (m)**

A concentration term expressed as number of moles of solute dissolved in 1000 g (1 kg) of solvent.

**mole fraction (X)**

A concentration term expressed as the ratio of number of moles of solute to the total number of moles (solute plus solvent).

**mononucleotide**

A monomer unit of a nucleic acid, consisting of an N-containing base, a sugar, and a phosphate group.

**nonelectrolyte**

A substance whose aqueous solution does not conduct an electric current.

**nucleic acid**

An unbranched polymer of mononucleotides that occurs as two types, DNA and RNA (deoxyribonucleic and ribonucleic acids), which differ chemically in the nature of the sugar portion of their mononucleotides.

**osmosis**

The process by which solvent flows through a semipermeable membrane from a dilute to a concentrated solution.

**osmotic pressure (Π)**

The pressure that results from the ability of solvent, but not solute, particles to cross a semipermeable membrane. The pressure required to prevent the net movement of solvent across the membrane.

**protein**

A natural, unbranched polymer composed of any of about 20 types of amino acid monomers linked together by peptide bonds.

**Raoult’s law**

A law stating that the vapor pressure of solvent above a solution equals the mole fraction of solvent times the vapor pressure of pure solvent:

**reverse osmosis**

A process for preparing drinkable water that uses an applied pressure greater than the osmotic pressure to remove ions from an aqueous solution, typically seawater.

**saturated solution**

A solution that contains the maximum amount of dissolved solute at a given temperature (prepared with undissolved solute present).

**semipermeable membrane**

A membrane that allows solvent, but not solute, to pass through.

**soap**

The salt formed in a reaction between a fatty acid and a strong base, usually a Group 1A(1) or 2A(2) hydroxide.

**solubility (S)**

The maximum amount of solute that dissolves in a fixed quantity of a particular solvent at a specified temperature.

**solute**

The substance that dissolves in the solvent.

**solvation**

The process of surrounding a solute particle with solvent particles.

**solvent**

The substance in which one or more solutes dissolve.

**strong electrolyte**

A substance that is a good conductor of electric current in solution because it dissociates or ionizes completely.

**supersaturated solution**

An unstable solution in which more solute is dissolved than in a saturated solution.

**suspension**

A heterogeneous mixture containing particles that are visibly distinct from the surrounding fluid.

**Tyndall effect**

The scattering of light by a colloid.

**unsaturated solution**

A solution in which more solute can be dissolved at a given temperature.

**vapor pressure lowering (ΔP)**

The lowering of the vapor pressure of a solvent caused by the presence of dissolved solute particles.

**volume percent [% (v/v)]**

A concentration term defined as the volume of solute in 100. volumes of solution.

**wastewater**

Used water, usually containing industrial and/or residential waste, that is treated before being returned to the environment.

**water softening**

The process of replacing the hard-water ions Ca2+ and Mg2+ with Na+ ions.

**weak electrolyte**

A substance that is a poor conductor of electric current in solution because it only partially dissociates or ionizes.