pH&alkalinity - pH and Alkalinity URI URI WATERSHED...

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Neutral 0 2 4 More Acidic More Basic Strong hydro- chloric acid Vinegar Tomato juice Urine, saliva Orange juice Black coffee Sea water Baking soda Milk of Magnesia Soapy water Ammonia Bleach Draino 1 1 13 12 11 10 9 7 8 6 5 4 3 URIWW-3, July 2004 URI pH and Alkalinity URI WATERSHED WATCH, Cooperative Extension College of the Environment and Life Sciences (CELS) Department of Natural Resources Science (NRS) Coastal Institute in Kingston, 1 Greenhouse Road, Kingston, Rhode Island 02881-0804 Water quality standards for pH? The U.S. E.P.A. considers lakes with pH less than 5 “acidified.” Aquatic organisms may be stressed in such acidified lakes. The RI Department of Environ- mental Management (DEM) has a fresh water pH criteria of 6.5 – 9.0 or as what occurs naturally. The sea water pH criteria is 6.5 – 8.5, but not more than 0.2 units outside the normally occurring range. Kelly Addy, Linda Green, and Elizabeth Herron What is pH? pH, one of the most common analyses in soil and water testing, is the standard measure of how acidic or alkaline a solution is. It is measured on a scale from 0 – 14 (Figure 1). pH of 7 is neutral, pH less than 7 is acidic, and pH greater than 7 is basic. The closer pH gets to 1, the more acidic. The closer pH gets to 14, the more basic. Examples of the pH of some common items are listed in Figure 1. Acids and bases are two extremes like hot and cold. Mixing acids and bases together can even out the extreme effects much like mixing hot and cold water to even out water temperature. The pH scale is logarithmic, which means that a unit decrease in pH equals a ten fold increase in acidity. For instance, tomato juice (pH 4) is ten times more acidic than black coffee (pH 5). Hydrogen (H + ) ions (ions are atoms or groups of atoms with negative or positive charge) control acidity levels. pH measures the concentration of H + and hydroxide (OH - ) ions which make up water (H 2 O): H + + OH - = H 2 O When the two ions are in equal concentration, the water is neutral, whereas the water is acidic if H + > OH - and basic when OH - > H + . Figure 1: pH scale and examples of solutions at particular pH’s. Why is pH important? Aquatic organisms need the pH of their water body to be within a certain range for optimal growth and survival. Although each organism has an ideal pH, most aquatic organisms prefer pH of 6.5 – 8.0. Outside of this range, organisms become physio- logically stressed. Reproduction can be impacted by out-of-range pH, and organisms may even die if the pH gets too far from their optimal range. In addition to directly affecting the physiology of aquatic organisms, additional aspects of lake dy- namics are influenced by pH. Low pH can cause the release of toxic elements and compounds from sediments into the water where they may be taken up by aquatic animals or plants. Changes in pH also influence the availability of plant nutrients, such as phosphate, ammonia, iron and trace met- als, in the water.
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Page 2 pH and Alkalinity, URI Watershed Watch How is pH measured?
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