What is pH?

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What is pH?
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What is pH?

• pH is the measurement used to determine whether a
  substance is acidic or basic
• Chemicals may be classed as acids or bases.
• Things that are neither acids nor bases are
  neutral.
• When have you seen pH measurements being used?

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Acids

• Often taste sour
• Strong acids can burn skin eyes
• Strong acids can dissolve metals
• Examples
• Lemon juice
• Vinegar
• Car battery acid (dangerous!)

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Bases

• Can taste bitter, sweetish, or salty
• Strong bases can burn skin eyes
• Bases react more easily with protein than with
  metal they are often used for cleaning
• Examples
• Milk
• Baking soda
• Soap
• Drain cleaner (dangerous!)

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What substance is neutral?

• WATER!

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• A special name is given to the acid or base
  characteristic that a substance has
• It is called pH
• p stands for potential and H stands for
  hydrogen
• hence, the potential of a substance to attract
  hydrogen ions

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pH scale
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pH scale

• pH scale ranges from 0 -14
• pH 7 is neutral neither acid nor base
• Pure water is pH 7
• Low pH (0-6.9) acid
• High pH (7.1-14) base
• The closer to the ends of the scale, the stronger
  the solution is

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Importance of pH
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How is pH measured?

• How much H versus OH- is present within a
  solution
• H (hydrogen ion)
• OH- (hydroxide ion)
• Ions form because of dissociation

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How is pH measured?
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Understanding pH measurements

• Each pH unit is 10 times as large as the previous
  one
• A change of 2 pH units means 100 times more basic
  or acidic

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pH indicators

• pH indicator is a halochromic chemical compound
  that is added in small amounts to a solution so
  pH can be determined visually.
• Chemical detector for H
• Color of solution changes depending on pH
• Litmus paper
• Digital pH indicators
• Natural indicator
• Hydrangeas (blue in more acidic soil pink/red in
  alkaline soil)

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Buffers

• Homework What is a buffer? How does it relate to
  pH?
• Read this tutorial from Carnegie Mellon
  University
• http//chemcollective.org/activities/tutorials/buf
  fers/buffers3