pH and Acid-Base Indicators

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pH and Acid-Base Indicators
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The pH Scale

• The power of hydrogen
• Expresses the concentration of H

Acidic Neutral Basic
H gt OH- H OH- H lt OH-
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Ionization of Water

• Pure water is neutral (pH 7)
• Why?
• You might think that pure water contains no H or
  OH-
• However, even pure water ionizes slightly
• At SATP, 2 in every billion water molecules
  ionize
• H2O(l) ? H(aq) OH-(aq)
• i.e H in pure water is 1.0 X 10-7 mol/L

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Relating H to pH
H 10-pH
Acidic Neutral Basic
H gt 1.0 X 10-7 M pH lt 7 i.e. 1.0 X 10-6 M 1.0 X 10-2 M H 1.0 X 10-7 M pH 7 H lt 1.0 X 10-7 M pH gt 7 i.e. 1.0 X 10-8 M 1.0 X 10-12 M
pH -logH
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Acid-Base Indicators

• A common method for determining pH of a solution
  is to use an indicator
• Indicators respond to changes in H (change
  colour)

Universal Indicator
Litmus Paper
Cabbage Juice
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Bromothymol blue
Phenolphthalein
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Homework

• P. 371 2-6
• P. 371 9,10
• P. 375 1-4,6cd,12
• http//www.titrations.info/acid-base-titration-ind
  icators-preparationcongo-red

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Bromothymol blue
Universal Indicator