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Unformatted text preview: different colors: Acid-Base Indicators Phenolpthalein is used in acid-base titrations for its colorless-to-pink transition at pH 8.0 -9.6 Acid-Base Indicators The equilibrium constant for the acid-type indicator can be written and rearranged to give [H 3 O + ]: [H 3 O + ] determines the ratio, hence the color developed by the solution Acid-Base Indicators Human eye not sensitive to color differences when ratio is greater than about 10 or less than about 0.1: For full acid color: For full basic color: Acid-Base Indicators If the negative logarithms are taken for the two previous expressions, the indicator pH range can be obtained: If an indicator has pK a = 5, it shows a complete color change when the pH of the solution changes from 4-6. Acid-Base Indicators Acid-Base Indicators Pick an indicator with transition range near or includes equivalence point pH...
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This note was uploaded on 02/15/2010 for the course CHEM 316 taught by Professor Soriaga during the Fall '08 term at Texas A&M.
- Fall '08