Science of Water : Concepts and Applications

Water Chemistry 99
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Solids—Substances that maintain defi nite size and shape. Solids in water fall into one of
the following categories:
1. Dissolved
2. Colloidal
3. Suspended
Dissolved solids are in solution and pass through a fi lter. The solution consisting of the
dissolved components and water forms a single phase (a homogenous solution).
Colloidal solids (sols) are uniformly dispersed in solution but they form a solid phase
that is distinct from the water phase.
Suspended solids are also a separate phase from the solution. Some suspended solids
are classifi ed as settleable solids. Placing a sample in a cylinder and measuring
the amount of solids that have settled after a set amount of time determines settleable
solids. The size of solids increases going from dissolved solids to suspended
solids.
Liquids—Having a defi nite volume, but not shape, liquids will fi ll containers to certain
levels and form free level surfaces.
Gases—Of neither defi nite volume nor shape, they completely fi ll any container in which
they are placed.
Element—The simplest form of chemical matter. Each element has chemical and physical
characteristics different from all other kinds of matter.
Compound—A substance of two or more chemical elements chemically combined. Examples:
water (H 2 O) is a compound formed by hydrogen and oxygen. Carbon dioxide (CO 2 )
is composed of carbon and oxygen.
Mixture—A physical, not chemical, intermingling of two or more substances. Sand and
salt stirred together form a mixture.
Atom—The smallest particle of an element that can unite chemically with other elements.
All the atoms of an element are the same in chemical behavior although they may differ
slightly in weight. Most atoms can combine chemically with other atoms to form
molecules.
Molecule—The smallest particle of matter or a compound that possesses the same composition
and characteristics as the rest of the substance. A molecule may consist of a single
atom, two or more atoms of the same kind, or two or more atoms of different kinds.
Radical—Two or more atoms that unite in a solution and behave chemically as if a single
atom.
Solvent—The component of a solution that does the dissolving.
Solute—The component of a solution that is dissolved by the solvent.
Ion—An atom or group of atoms that carries a positive or negative electric charge as a
result of having lost or gained one or more electrons.
Ionization—The formation of ions by splitting of molecules or electrolytes in solution.
Water molecules are in continuous motion, even at lower temperatures. When two water
molecules collide, a hydrogen ion is transferred from one molecule to the other. The water
molecule that loses the hydrogen ion becomes a negatively charged hydroxide ion. The
water molecule that gains the hydrogen ion becomes a positively charged hydronium ion.
This process is commonly referred to as the self-ionization of water.
Cation—A positively charged ion.
Anion—A negatively charged ion.
Organic—Chemical substances of animal or vegetable origin made of carbon structure.
Inorganic—Chemical substances of mineral origin.
Solids—As pertaining to water—suspended and dissolved material in water.
Dissolved solids—The material in water that will pass through a glass fi ber fi lter and
remain in an evaporating dish after evaporation of the water.