Appendix 1

DEFINITIONS AND REFERENCES FOR AQUEOUS GEOCHEMISTRY

Laurie Balistrieri

Acid: a substance containing hydrogen that gives free hydrogen ions (H+) when dissolved in water; e.g., hydrochloric acid (HCl), nitric acid (HNO3).  Strong acids release a greater proportion of their protons than weak acids.
Acidity: the base neutralizing capacity of an aqueous system or the capacity to donate protons.  Usually determined by titration with a standardized base to a reference pH.
Alkalinity: the acid neutralizing capacity (ANC) of an aqueous system or the capacity to accept protons.  Usually determined by titration with a standardized acid to a reference pH.
Adsorption: the attachment of dissolved substances (e.g., ions) to solid surfaces.
Aqueous geochemistry: the study of chemical reactions occurring between water and rocks.  
Base: a substance containing a hydroxyl group (-OH) that yields hydroxyl ions (OH-) when dissolved in water; e.g., potassium hydroxide (KOH), sodium hydroxide (NaOH).
Compounds: substances that are composed of two or more elements in the same proportions, e.g., calcium carbonate (CaCO3) or pyrite (FeS2)
Dissolution of minerals: the act or process of separating into component parts, e.g., dissolution of salt (sodium chloride; NaCl) by water forming dissolved sodium ions (Na+) and chloride ions (Cl-).
Elements: substances that are composed of atoms that exhibit unique and identical properties, e.g., Fe, Zn, or Cu; see the attached periodic table of elements.
Equilibrium: time-invariant, most stable state of a system at a given temperature and pressure.
Hydrolysis: reactions leading to an excess of protons (H+) or hydroxyl ions (OH-) in solution; e.g., hydrolysis of ferric Fe (Fe3+) where Fe3+ + 2H2O " Fe(OH)2+ + 2H+.
Ion: an atom or group of atoms that carries a negative or positive charge as a result of having gained or lost one or more electron.  Positive ions are called cations and negative ions are called anions.
Kinetics: rates of change in a physical or chemical system.
Neutralization: reactions between acid and bases that result in neither acidic nor basic conditions.
Oxidation half-reactions: reactions that involve the loss of electrons from an atom or atoms.
pH: the negative, base-10 logarithm of the hydrogen ion activity [pH = - log (H+)]; pH values of most natural waters lie between 4 and 9 (e.g., pHseawater= 8.1-8.3).  The lowest observed pH values, including negative values, are found in systems where pyrite is being oxidized.
Precipitation of minerals: reactions where dissolved ions combine to form insoluble solids.
Reduction half reactions: reactions that involve the gain of electrons by an atom or atoms.
Reduction-oxidation (redox) reactions: reactions that involve both oxidizing agents (a substance that accepts electrons) and reducing agents (a substance that donates electrons).

REFERENCE BOOKS
Brownlow, A.H., 1979, Geochemistry: Prentice-Hall, 498 p.
Drever, J.I., 1988, The Geochemistry of Natural Waters: Prentice Hall, 437 p.
Krauskopf, K.B., and Bird, D.K., 1995, Introduction to Geochemistry: McGraw-Hill, 647 p.
Langmuir, D., 1997, Aqueous Environmental Geochemistry: Prentice-Hall, 600 p.
Morel, F.M.M., and Herring, J.G., 1993, Principles and Applications of Aquatic Chemistry: Wiley-Interscience, 588 p.
Stumm, W., and Morgan, J.J., 1996, Aquatic Chemistry: Wiley-Interscience, 1022 p.




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