The Most Common Chemical Terms

Absolute zero is −273.15°C or 0 Kelvin. It is the lowest possible temperature. Theoretically, at absolute zero, atoms stop moving.

(1) The physical or chemical process by which a substance in one state becomes incorporated into and retained by another substance of a different state. Absorption differs from adsorption in that the first substance permeates the entire bulk of the second substance, rather than just adhering to the surface. (2) The process by which matter (typically electrons bound in atoms) takes up the energy of electromagnetic radiation and transforms it into any of various types of internal energy, such as thermal energy. This type of absorption is the principle on which spectrophotometry is based.

Any substance capable of giving up a proton; a substance that ionizes in solution to give the positive ion of the solvent; a solution with a pH measurement less than 7.

Treatment of a substance by heat, radiation, or activating reagent to produce a more complete or rapid chemical or physical change.

The chemical adhesion of atoms, ions, or molecules of one substance (either a gas, liquid, or dissolved solid) to the surface of another substance, resulting in a film of the first substance being weakly bonded to the interface between the two substances. Adsorption differs from absorption in that it is exclusively a surface phenomenon, while absorption involves entire volumes of materials.

Living or occurring only in the presence of oxygen.

Any class of organic compounds containing the hydroxyl group, OH. Specifically, the term is applied to ethyl alcohol (C₂H₅OH).

The capacity of water to neutralize acids, a property imparted by the water's content of carbonate, bicarbonate, hydroxide, and on occasion borate, silicate, and phosphate. It is expressed in milligrams per liter of equivalent calcium carbonate (mg/l CaCO₃).

Any of two or more physical forms in which an element can exist.

A metallic material, such as steel, brass, or bronze, consisting of a mixture of two or more metals or of metallic elements with nonmetallic elements. Alloys often have physical properties markedly different from those of the pure metals.

Any of a group of organic compounds containing one or more amino groups, -NH₂, and one or more carboxyl groups, -COOH. The alpha-amino acids RCH(NH₂)COOH (where R is either hydrogen or an organic group) are the component molecules of proteins; some can be synthesized in the body (nonessential amino acids) and others cannot and are thus essential components of the diet (essential amino acids).

Living or occurring only in the absence of free oxygen.

With all water removed, especially water of crystallization.

A unit of length, used especially in expressing the length of light waves, equal to one ten-thousandth of a micron, or one hundredth-millionth of a centimeter (1 x 10E-8 cm).

Ion having a negative charge; an atom with extra electrons. Atoms of non-metals, in solution, become anions.

The positive electrode in an electrolytic cell.

The smallest particle of an element which can exist alone or enter into a chemical combination.

Quantitative chemical method used for the analysis of elemental constituents.

The mass of an atom expressed in atomic mass units (amu); the total number of protons and neutrons in the nucleus.

A unit of mass equal to 1/12 the mass of the carbon isotope with mass number 12, approximately 1.6604 x 10E-24 gram.

The number of protons in the nucleus of an atom.

The average weight of an atom of an element, usually expressed relative to one atom of the carbon isotope taken to have a standard weight of 12.

Any substance which contains hydroxyl (OH) groups and furnishes hydroxide ions in solution; a molecular or ionic substance capable of combining with a proton to form a new substance; a substance that provides a pair of electrons for a covalent bond with an acid; a solution with a pH of greater than 7.

The quantity of oxygen used in the biochemical oxidation of organic matter in a specified time, at a specified temperature, and under specified conditions.

The temperature at which a liquid boils at a given pressure, usually atmospheric pressure at sea level; the temperature at which the vapour pressure of a liquid equals the external pressure.

Random movement of microscopic particles suspended in a fluid, caused by bombardment of the particles by molecules of the fluid. First observed in 1827, it provided strong evidence in support of the kinetic theory of molecules.

A solution selected or prepared to minimize changes in hydrogen ion concentration which would otherwise occur as a result of a chemical reaction.

The checking, adjusting, or systematic standardizing of the graduations of a quantitative measuring instrument.

The quantity of heat necessary to raise the temperature of 1 gram of water 1°C at 1 atmosphere pressure.

Any of a large group of organic compounds, including sugars, such as sucrose, and polysaccharides, such as cellulose, glycogen, and starch, that contain carbon, hydrogen, and oxygen, with the general formula Cm(H₂O)n: an important source of food and energy for animals.

A substance that alters the velocity of a chemical reaction and may be recovered essentially unaltered in form and amount at the end of the reaction.

The negative electrode in an electrolytic cell; the electrode by which electrons enter a device from an external circuit.

A positively charged atom or group of atoms, or a radical which moves to the negative pole (cathode) during electrolysis.

Capable of destroying or eating away by chemical action; a hydroxide of a light metal.

Codium hydroxide, NaOH.

A process in which a neutron colliding with an atomic nucleus causes fission and the ejection of one or more other neutrons, which induce other nuclei to split.

The use of a standard chemical analytical procedures to determine the concentration of a specific analyte in a sample, or qualitatively or quantitatively measure a specific parameter of a sample.

A representation of a chemical reaction using symbols of the elements to indicate the amount of substance, usually in moles, of each reactant and product.

The destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of a floc-forming chemical.

The amount of oxygen required for the chemical oxidation of organics in a liquid; a chemical test that determines the oxygen equivalent of the amount of organic matter oxidizable by potassium dichromate in a 50% sulfuric acid solution.

(1) The process of utilizing chemicals to produce a separable solid phase within a liquid medium; in analytical chemistry, precipitation is used to separate a solid phase in an aqueous solution. (2) The process of softening water by the addition of lime and soda ash as the precipitants.

The technique of separating and analysing the components of a mixture of liquids or gases by selective adsorption in, for example, a column of powder (column chromatography) or on a strip of paper (paper chromatography).

The composite wastewater treatment process consisting of flash mixing of coagulants, pH adjusting chemicals, and/or polyelectrolytes, flocculation, and sedimentation.

The clumping of particles in order to settle out impurities; often induced by chemicals such as lime or alum.

A chemical process in which two compounds, such as sodium and chlorine, react together to produce heat and light.

The use of chelating or sequestering agents to form relatively loose chemical bonding as a means of treating certain pollutants such as nickel, copper, and cobalt.

Two of more elements combined; a substance having different properties than of the elements used.

In solutions, the mass, volume, or number of moles of solute present in proportion to the amount of solvent or total solution Common measures are: molarity, normality, percent, molality, and by specific gravity scales.

A type of reaction in which two organic molecules combine to form a larger molecule as well as a simple molecule such as water, methanol, etc.

A measure of the conducting power of a solution equal to the reciprocal of the resistance. The resistance is expressed in ohms.

Ability of a material to carry current or heat.

A general term signifying the introduction into water of microorganisms, chemicals, wastes or sewage which renders the water unfit for its intended use.

A process in which a solid, esp a metal, is eaten away and changed by a chemical action, as in the oxidation of iron in the presence of water by an electrolytic process.

A type of chemical bond involving the sharing of electrons between atoms in a molecule, esp the sharing of a pair of electrons by two adjacent atoms.

Critical mass is the minimum quantity of radioactive material needed to cause a nuclear chain reaction.

The critical point is the endpoint of the liquid-vapor line in a phase diagram, past which a supercritical liquid forms. At the critical point, the liquid and vapor phases become indistinguishable from one another.

A piece of solid substance, such as quartz, with a regular shape in which plane faces intersect at definite angles, due to the regular internal structure of its atoms, ions, or molecules.

The process in which crystals are formed either from something that has been melted or from a solution.

To remove the liquid portion of a settled mixture without disturbing the sediment.

That which can be reduced, broken down or chemically separated.

The time allowed for solids to collect in a settling tank. Theoretically detention time is equal to the volume of the tank divided by the flow rate.

The temperature at which the condensation of a vapor begins; the term is usually applied to condensation of moisture from the water vapor in the atmosphere.

The separation of a colloid from a substance in solution by allowing the solution to diffuse through a semipermeable membrane.

The random thermal motion of atoms, molecules, clusters of atoms, etc, in gases, liquids, and some solids.

The biochemical decomposition of organic matter which results in the formation of mineral compounds and simple organic compounds.

Deionized water, having had all the ions removed.

The thinning agent used to dilute a fluid, usually water.

To thin out, or having been thinned out; less than full strength.

A component that readily passes current in one direction but opposes current flow in the opposite direction.

Effective killing by chemical or physical processes of all organisms capable of causing infectious disease. Chlorination is the disinfection method commonly employed in sewage-treatment processes.

The oxygen dissolved in sewage, water, or other liquid, usually expressed in milligrams per liter or percent of saturation. It is the test used in BOD determination. dissolved solids: the total amount of dissolved material, organic and inorganic, contained in water or wastewater. Excessive dissolved solids make water unpalatable for drinking and unsuitable for industrial use. Measurements are expressed as ppm or mg/L.

The process of heating a liquid to its boiling point, removing the vapors through a cooling and condensing apparatus, and finally collecting the condensed liquid in a separate receiver. It is commonly used for the separation of two or more liquids in a mixture, or for the separation of the solvent from dissolved substances.

Water that has been purified by distillation (boiling the water off as steam and condensing it back to a liquid, leaving the impurities behind). Having been boiled, it is also sterile.

Ethylenediaminetetraacetic acid (or its salts). A standard method of measuring the hardness of a solution

A liquid that has passed through a processing operation.

An element in a semiconducting device that emits, collects, or controls the movement of electrons or holes.

The conduction of electricity by a solution or melt, esp the use of this process to induce chemical changes.

The sub-atomic particle, with a negative charge, that orbits the nucleus of an atom.

A substance that cannot be resolved into two or more other substances; a substance made up of atoms with the same atomic number.

A liquid system in which one liquid is finely dispersed in another liquid in such a manner that the two will not separate through the action of gravity alone.

Endothermic describes a process that absorbs heat. Endothermic reactions feel cold.

That stage in the titration at which an effect, such as a color change, occurs, indicating that a desired point in the titration has been reached.

The addition of nitrogen, phosphorous, and carbonaceous compounds, or other nutrients into a lake or other waterway that greatly increases the growth potential for algae and other aquatic plants. Most frequently, enrichment results from the inflow of sewage effluents or from agricultural runoff.

Entropy is a measure of the disorder or randomness in a system.

Equilibrium occurs in reversible reactions when the forward rate of the reaction is the same as the reverse rate of the reaction.

The equivalence point is when the solution in a titration is completely neutralized. It is not the same as the endpoint of a titration because the indicator may not change colors precisely when the solution is neutral.

When a liquid changes to a vapor, caused by an increase in temperature and/or a decrease in pressure.

Exothermic describes a process that gives off heat.

A chemical reaction in which a ferment causes an organic molecule to split into simpler substances, esp the anaerobic conversion of sugar to ethyl alcohol by yeast.

The process of separating solids from a liquid by means of a porous substance through which only the liquid can pass.

The act or process of splitting or breaking into parts.

The process of removing finely divided particles from a liquid suspension by agitating the liquid with gas bubbles thus increasing the buoyancy of the particles, and concentrating them at the surface of the liquid medium.

The process of separating suspended solids from wastewater by chemical creation of a coagulated, or flocculent masses.

Usually expressed as liters/minute (gallons/minute) or liters/day. Design flowrate is that used to size the wastewater treatment process. Peak flowrate is 1.5 to 2.5 times design and relates to the hydraulic flow limit and is specified for each plant.

A substance which yields readily to any force which tends to alter its shape; fluids possess no definite shape; the term includes both liquids and gases.

A material used to promote joining of metals in soldering.

An expression of chemical composition, using symbols and figures.

A protective device containing a short piece of wire that melts and breaks when current through it exceeds a rated value, thus de-energizing the circuit.

A fluid having neither independent shape nor volume, but tending to expand indefinitely. The word is often used to denote anesthetics, combustibles (gasoline), poisonous materials, etc., whether liquid or solids at ordinary temperatures.

Any of the chemical elements fluorine, chlorine, bromine, iodine, and astatine. They are all monovalent and readily form negative ions.

A characteristic of water, imparted by salts of calcium, magnesium, and iron, such as bicarbonates, carbonates, sulfates, chlorides, and nitrates that cause curdling of soap, deposition of scale in boilers, damage in some industrial process, and sometimes objectionable taste. It may be determined by a standard laboratory procedure or computed from the amounts of calcium and magnesium as well as iron, aluminum, manganese, barium, strontium, and zinc; expressed as equivalent parts per million of calcium carbonate.

A general term given to the ions of metallic elements such as copper, zinc, chromium, and aluminum. They are removed from wastewater by forming an insoluble precipitate (usually a metallic hydroxide).

A chemical compound containing only hydrogen and carbon; the largest source of hydrocarbons comes from petroleum crude oil.

The infusing of unsaturated or impure hydrocarbons with hydrogen gas at controlled temperatures and pressures for the purpose of obtaining saturated hydrocarbons and/or removing various impurities such as sulfur and nitrogen.

A chemical reaction in which a compound reacts with water to produce other compounds.

A compound that changes color at a particular pH, or over a particular narrow range of pH, used to show titration end points.

Having only a limited ability to react chemically; unreactive.

Relating to or denoting chemical compounds that do not contain carbon.

An isolated electron or positron; an atom or molecule which by loss or gain of one or more electrons has acquired a net electric charge.

The chemical bond between two oppositely charged ions formed when one atom transfers electrons to another atom, as in the formation of sodium chloride; electrovalent bond.

A chemical reaction in which mobile hydrated ions of a solid are exchanged, equivalent for equivalent, for ions of like charge in solution. The process can be used to remove ionic pollutants from wastewater.

A process by which a neutral atom or molecule loses or gains electrons, thereby acquiring a net charge and becoming an ion; occurs as the result of the dissociation of the atoms of a molecule in solution or of a gas in an electric field.

Chemical compound that has the same number, and kinds of atoms as another compound, but a different structural arrangement of the atoms.

One of two or more atoms with the same atomic number that contain different numbers of neutrons.

A substance in a physical state in which it does not resist change of shape but does resist change of size.

A test to establish the acidity or alkalinity of a mixture.

The quantity of matter in a body as measured by its resistance to a change in acceleration; different but proportional to weight.

The total number of protons and neutrons in an atomic nucleus.

The temperature at which a solid turns into a liquid. It is equal to the freezing point.

Any of a number of chemical elements, such as iron or copper, that are often lustrous ductile solids, have basic oxides, form positive ions, and are good conductors of heat and electricity.

A nonmetallic element, such as arsenic or silicon, that has some of the properties of a metal.

Organisms (microbes) observable only through a microscope; larger, visible types are called macroorganisms.

Any of a class of naturally occurring solid inorganic substances with a characteristic crystalline form and a homogeneous chemical composition.

A substance consisting of two or more substances mixed together without any chemical bonding between them.

A solution concentration having a mole of solute per 1,000 grams of solvent, usually water.

A measure of solution concentration expressed in moles of solute per 1,000 grams of solvent.

A solution concentration having one mole of solute per liter of solution.

A measure of solution concentration expressed in moles of solute per liter of solution.

An amount of a substance weighing the number of grams equal to the total atomic weight in one molecule (or atom). Equivalent to gram-atomic, gram-molecular, and gram-formula weights.

The sum of the atomic weights of all the atoms in a molecule.

The simplest structural unit of a substance that retains the properties of the substance, and is composed of one or more atoms.

A compound whose molecules can join together to form a polymer.

Neither acidic nor alkaline.

An uncharged sub-atomic particle, with a mass nearly equal to that of a proton. Present in the nucleus of all atoms except hydrogen.

The suspended matter which neither settles nor floats to the surface of water in a period of one hour.

Wastewater matter that will stay in suspension for an extended period of time. Such period may be arbitrarily taken for testing purposes as one hour.

A solution concentration of one gram equivalent per liter of solution.

A measure of solution concentration expressed in equivalent weights of solute per liter of solution.

A fundamental group of atoms in a molecule serving as the base structure for related compounds and remaining unchanged during most chemical reactions.

Materials which are considered essential to the support of biological life.

Any of a number of viscous liquids with a smooth sticky feel. They are usually flammable, insoluble in water, soluble in organic solvents, and are obtained from plants and animals, from mineral deposits, and by synthesis. They are used as lubricants, fuels, perfumes, foodstuffs, and raw materials for chemicals.

Any naturally occurring mineral or aggregate of minerals from which economically important constituents, esp metals, can be extracted.

Chemical compounds based on carbon chains or rings, and also containing hydrogen with or without oxygen, nitrogen, or other compounds.

A chemical agent that oxidizes.

In a broad sense oxidation is the increase in positive valence of any element in a substance. On the basis of the electron theory, oxidation is a process in which an element loses electrons. In a narrow sense, oxidation means the chemical addition of oxygen to a substance.

Oxygen in molecular form with three atoms of oxygen forming each molecule (O₃). Atmospheric oxygen is molecular in form but each molecule contains only two atoms of oxygen. Ozone is formed by passing high voltage electric charges through dry air. The third atom of oxygen in each molecule of ozone is loosely bound and is easily released, thus making it a powerful oxidant; used to purify water and treat industrial wastes.

A table in which the elements are commonly arranged in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding eight families or groups of elements. Within each group there is a gradation of chemical and physical properties, but in general a similarity of chemical behavior. From group to group, however, there is a progressive shift of chemical behavior from one end of the table to the other.

The negative logarithm of the hydrogen ion concentration (-log10[H+]) where H+ is the hydrogen-ion concentration in moles per liter. Neutral water has a pH value of 7.

A naturally occurring or synthetic compound, such as starch or Perspex, that has large molecules made up of many relatively simple repeated units.

The discrete particles of material separate from the liquid solution.

A sub-atomic particle, positively charged, in the nucleus of atoms.

Chemical determination of the amounts or proportions of constituents in a substance.

An atom or group of atoms with at least one unpaired electron.

The spontaneous emission of radiation from atomic nuclei. The radiation can consist of alpha, beta, and gamma radiation.

A process that involves changes in the structure and energy content of atoms, molecules, or ions but not their nuclei.

A chemical substance used to cause a reaction for the purpose of chemical analysis.

Chemical reaction in which an atom or molecule gains an electron; decrease in positive valence; addition of hydrogen to a molecule.

(1) The relative concentration of salts, usually sodium chloride, in a given water. It is usually expressed in terms of the number of ppm of chloride. (2) A measure of the concentration of dissolved mineral substances in water.

Any compound formed by combination of any negative ion (except hydroxide) with any positive ion (except hydrogen or hydronium); the precipitate produced as the result of neutralization of an acid with a base.

The conversion of an ester heated with an alkali into the corresponding alcohol and acid salt; specif., this process carried out with fats (glyceryl esters) to produce soap.

(1) In organics, a chemical compound with all carbon bonds satisfied; it does not contain double or triple bonds and thus cannot add elements or compounds. (2) In liquids, a solution that contains enough of a dissolved solid, liquid, or gas so that no more will dissolve into the solution at a given temperature and pressure.

The deposition of suspended matter carried by water, wastewater, or other liquids, by gravity. It is usually accomplished by reducing the velocity of the liquid below the point at which it can transport the suspended material. Also called settling.

Particles of debris and fine matter heavy enough to settle out of wastewater.

(Of a substance) capable of being dissolved, esp easily dissolved in some solvent, usually water.

The substance that is dissolved to form a solution.

A liquid (solvent) that contains a dissolved substance (solute).

A liquid used to dissolve another substance.

A comparison by weight to an equal volume of pure water, at a standard temperature.

A solution containing a known, precise concentration of an element or chemical compound, often used to calibrate analytical chemistry measurement devices.

The property, due to molecular forces in the surface film, that tends to contract the liquid into a form having the least surface/volume ratio.

A surface-active substance, such as a detergent or soap, that lowers the surface tension of a solvent (usually water).

(1) Solids in suspension in water, wastewater or effluent. (2) Solids in suspension that can be removed readily by standard filtering procedures in a laboratory.

(1) Solids that either float on the surface of, or are in suspension in, water, wastewater, or other liquids, and which are largely removable by laboratory filtering. (2) The quantity of material removed from wastewater in a laboratory test, as prescribed in "Standard Methods" and referred to as nonfilterable residue.

A dispersion of fine solid or liquid particles in a fluid, the particles being supported by buoyancy.

The process of producing a compound by a chemical reaction or series of reactions, usually from simpler or commonly available starting materials.

A method of analyzing the composition of a solution by adding known amounts of a standardized solution until a given reaction (color change, precipitation, or conductivity change) is produced.

Any element belonging to one of three series of elements with atomic numbers between 21 and 30, 39 and 48, and 57 and 80. They have an incomplete penultimate electron shell and tend to exhibit more than one valency and to form complexes.

(1) A condition in water or wastewater caused by the presence of suspended matter, resulting in the scattering and absorption of light rays. (2) A measure of fine suspended matter in liquids. (3) an analytical quantity usually reported in turbidity units (NTU/FNU, FTU, JTU) determined by measurements of light diffraction.

Any chemical compound with more than one bond between adjacent atoms, usually carbon, and thus reactive toward the addition of other atoms at that point; for example: olefins, diolefins, and unsaturated fatty acids.

A property of atoms or groups, equal to the number of atoms of hydrogen that the atom or group could combine with or displace in forming compounds.

Weak electrostatic forces between atoms and molecules caused by transient distortions in the distribution of electrons in the interacting atoms or molecules.

The resistance offered by a fluid (liquid or gas) to flow. The viscosity is a characteristic property and is a measure of the combined effects of adhesion and cohesion.

The quantity of solid in water, wastewater or other liquids, lost on ignition of the dry solids at 600°C.