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Lab _1 - pH Revised 1-25-2011

Lab _1 - pH Revised 1-25-2011 - Revised January 2011...

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Revised January 2011 Page 1 of 5 1/25/2011 EXERCISE 1 MEASURING pH The pH of a solution is a measure of the amount of acidity or alkalinity (basicity) in the solution. Mathematically, the pH is defined as the negative logarithm of the concentration of hydrogen ions, [H + ]. pH= -log[H + ] Water is comprised of molecules of H 2 O that ionize (or break apart) in solution as equal amounts of positive hydrogen ions (H + ) and negative hydroxyl (OH - ). The range of pH is from 0 to 14. When there are equal amounts of H + ions and OH - ions present, th e solution is “neutral” with respect to the net charges and the pH is 7.0. If the H + ion concentration is greater than the OH - ions, the solution is ACIDIC; if the OH - ion concentration is greater, the solution is ALKALINE, or BASIC. Remember that pH is expressed as a negative logarithm of H + concentration, so when the H + concentration increases , the pH goes down . The higher the [H + ], the lower the pH, and thus a low pH is an acidic pH. Temperature can have a marked effect upon pH. The pH scale runs from 0-14. Since pH is logarithmically based, an increase in pH by 1 means that the solution is 10 times more basic, while a decrease in pH by 1 means that the solution is 10 times more acidic. For example: pH 6 is 10x more acidic than pH 7 pH 5 is 100x more acidic than pH7 pH 4 is 1000x more acidic than pH7 etc. Measuring pH is one of the basic requirements in understanding and solving several environmental problems. For example, acid rain is a major global environmental problem affecting all industrial countries, especially the US, Canada, Germany, Great Britain, and Scandinavian countries. In the US, the northeastern states have the worst concentration of acid rain. This is a direct result of industrialization.
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