Definitions--Aquatic Chemistry

The ability to neutralize OH- ions. This may be due to mineral acids in the water, and to hydrolysis of some metal ions
alkalinity, phenolphthalein alkalinity, total alkalinity
The ability to neutralize H+ ions. High alkalinity water often has a high pH and high dissolved solids. Alkalinity is primarily due to carbonate, bicarbonate and carbon dioxide dissolved in the water. Phenolphthalein alkalinity is named for the indicator used in the titration of the water with acid. At the phenolphthalein endpoint, about pH 8, the carbonate content is converted to bicarbonate. For total alkalinity, methyl orange is used, and the titration is carried to a pH of 4.3, at which point both the carbonate and bicarbonate have been titrated to CO2, or H2CO3, carbonic acid. 

BOD Biological Oxygen Demand-determined by saturating the water sample with oxygen, and measuring the oxygen content after 5 days incubation. The BOD is the concentration of oxygen used up. The sample may need to be inoculated with bacteria, if it does not have a sufficient amount to begin with.

COD Chemical oxygen demand. Water sample is oxidized by refluxing with acidic potassium dichromate. Remaining dichromate is determined by titration. The amount of dichromate used up in the reaction is converted into an equivalent amount of oxygen to obtain the COD.

Particles suspended in a liquid, which are larger than molecular size but small enough to be moved about by molecular collisions. These particles do not settle under gravity. Their surface area is very large per gram, and the particles have a charge due to ions sorbed on the surface. This charge prevents coagulation or clumping of the particles and therefore, coagulation can be brought about by neutralizing the charge. 
A central molecule surrounded by ligand molecules attached by electrostatic attractions. They have a structure, but the bonds are often weak enough that the ligands can be readily exchanged in solution.
coordination number
The number of ligands usually coordinated to a central atom or ion
coordination sphere
The space around a central molecule, atom, ion, which is filled by the ligand species.
A molecule which has a definite separation between its center of positive charge and center of negative charge. Such a molecule is said to be polar. A polar species will be more attracted to a charged species than will a non-polar one.
equilibrium constant
An expression involving the concentrations of reactants and products involved in a reaction. This expression yields a constant value regardless of the concentrations. The constant changes only with temperature.
hardness, temporary hardness
Hardness is produced by calcium and magnesium in water. These ions cause a precipitate with soap. Temporary hardness is caused by bicarbonate and can be removed by boiling which converts the bicarbonate to carbon dioxide and calcium carbonate.
Henry's law
The solubility of a gas in a liquid can be calculated by Henry's law which states that the solubility of the gas is proportional to the partial pressure of the gas in contact with the liquid.
Water molecules are attracted to ions in water solution and coordinate around the ions, forming a sphere of hydration.
hydrogen bond
The hydrogen atoms in water are very positive, because the oxygen atom strongly withdraws the electrons in the O-H bonds. The hydrogen atoms on adjacent molecules are attracted to the oxygen atoms forming a bond which is stronger than the usual polar attraction, but less strong than a typical covalent bond. This accounts for the very high boiling point of water compared with other similar weight molecules.
inorganic carbon
The carbon containing compounds in water which are not organic compounds, carbonate and bicarbonate species promarily.
ligand, unidentate, bidentate
An organic compound containing metal atoms
partial pressure
pressure a gas in a mixture would exert if it was alone in the container. For example, the partial pressure of oxygen in air at 1 atmosphere pressure is 0.2 atm, because oxygen is 20% of the atmosphere.
-log[H+] where [H+] = concentration of H+in moles/liter
property of a molecule which describes the difference in location of the center of positive and center of negative charge on the molecule. A nonpolar compound has these centers coinciding. As they become further apart, the molecule becomes more polar.
determination of particular chemical forms of an element, rather than just the total element. Metals may be speciated by oxidation state (Cr(VI) vs. Cr(III), for example,) or by successively stronger extractions from a solid sample.

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