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pH What is pH? • pH is a measure of the acidity, [H+], or basicity (alkalinity), [OH-], of a solution. • The scale is typically measured from 0 to 14. • A pH value of 7 is considered to be neutral, neither acid nor base. pH Scale 0 14 7 Acidic [H+]>[OH-] Neutral [H+]=[OH-] Basic [OH-]>[H+] What is pH? • pH is a logarithmic function. That is, pH = -log10 [H+]. • This simply means that a change of one pH unit represents a 10 fold change in the acidity, e.g. pH 5 is ten times more acidic than pH 6. For the More Advanced Students pH = -log10 [H+] So if: pH = 5 Then 5 = -log10 [H+] -5 = log10 [H+] 10-5 = [H+] or [H+] = 10-5 M Measuring pH • pH paper • Digital meters pH levels in our lives Water on the Web http://wow.nrri.umn.edu/wow/ What affects pH? • pH can affect and be affected by atmospheric chemistry. – Dissolved CO2 – Other nonmetallic oxides • pH can affect and be affected by geological chemistry. – Dissolved minerals – Other sources of minerals • Buffering capacity – Determines the vulnerability of a system to pH changes Activity: Acids, Bases and Buffers • See handout • Use of Probes • SO What?? This is what… • Acid Precipitation • Mine tailings • Soils have different buffering capacities • Can exceed tolerance levels for plants and animals • Can corrode buildings and other infrastructure http://www.cleartheair.org/acidrain/ Acid Precipitation http://pubs.usgs.gov/gip/acidrain/2.html Acid Mine Drainage Seepage from an historical mine tailing deposition area. Whitewood Valley, South Dakota. USFWS photo by Joy Gober and Scott Larson. http://www.r6.fws.gov/contaminants/contaminants2.html Why is pH important? pH Some organisms can tolerate a wider pH range. Most Aquatic Animals Snails, Clams, Mussels Bass, Bluegill, Crappie Carp, Suckers, Catfish Plants Bacteria 0 1 2 3 4 5 6 State Water Resources Control Board-Citizen Monitoring http://www.swrcb.ca.gov/nps/docs/Ph.doc 7 8 9 10 11 12 13 14 German forest damaged by acid precipitation Germania - Effetti delle precipitazioni acide sulla foresta di Erzgebirge (CREDIT: © WWF-Canon / Mauri Rautkari) http://www.wwf.it/summit/photogallery.asp?P=4 More damage…