ACIDBASE

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ACID-BASE INDICATORS
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Acid-base indicators are weak Bronsted-Lowry
compounds that are different colors in acid and
base form.
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Acid-base indicators are all large organic
molecules. HIn ltgt H In- Color 1
Color 2
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Phenolphthalein Colorless acid form, HIn
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Phenolphthalein Pink base form, In-
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The color change occurs at a different pH for
different indicators.

• The pH at which the indicator changes color is
  dependent on the Ka of the indicator as a weak
  acid.

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HIn ltgt H In-
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Experiments have shown that the minimum amount of
change of HIn ltgt In- that can be detected
visually is
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(No Transcript)
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Thus, from the Henderson-Hasselbalch equation,
one can select an appropriate indicator for a
titration based upon the Ka of the indicator and
the pH at the equivalence point.
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What is the pH at the equivalence point of a
titration of 25.0 mL each of 0.10 M HCl and 0.10
M NaOH?
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What is the pH at the equivalence point of a
titration of 25.0 mL each of 0.10 M CH3COOH and
0.10 M NaOH?
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Phenolphthalein Ka 1 x 10-9 pH of
perceptible color change?