pH Scale

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pH Scale

• Determines concentration (strength) of an acid or
  base.
• Acids below 7
• Bases above 7

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pH Scale

• Indicators show the pH level in the lab.

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Click for indicator demo
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pH Scale

• pH is based on the concentration of the hydronium
  ion.

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m3/medialib/media_portfolio/text_images/CH15/FG15_
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pH Scale
pH is not a linear scale!!
pH -logH3O
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pH Scale

• Example If the concentration of hydronium ions
  is 3.0 x 10-4 M, what is the pH?
• pH -log3.0 x 10-4
• pH 3.5

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pH Scale

• What about changing pH toH3O
• H3O10-pH

• Example If the pH of a base is 12.5, what is
  H3O?

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pH Scale

• H3O 10-12.5
• 3.16 x 10-13 M
• But waitdoesnt a base give off OH-???

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Water as an Acid Base
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Water as an Acid Base

• Keq H3OOH-
• Water is neutral so pH 7.

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Water as an Acid Base

• H3O 1 x 10-7
• Also, H3O and OH- are equal since water is
  neutral

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Water as an Acid Base

• 1 x 10-14 H3OOH-
• This is known as Kw.
• (Equilibrium Water Constant)

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pOH scale

• When NH3 is dissolved in water, it gives off the
  Hydroxide Ion (OH-)

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pOH Scale

• pOH scale is reversed
• (0-7 are bases, 7-14 acids)
• pOH -logOH-

• OH-10-pOH

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pH pOH

• pH pOH 14

• Example

• If OH- for a base is 2.00 x 10-2 M, what is
  the pH?

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pH pOH

• pOH -log2.00 x 10-2
• pOH 1.70
• pH 1.70 14
• pH 12.3