19.2 Hydrogen Ions and Acidity

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19.2 Hydrogen Ions and Acidity
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Self-Ionization of Water

• Water is very polar
• When the water molecules collide too fast a
  proton can break off and two ions form
• H2O ? H OH-
• Usually the H ion reacts with an intact H2O
  molecule to form an hydronium ion H3O
• H H2O ? H3O

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Algebra Review

• 10000 104
• ___1___ 10-4
• 10000
• Which number is larger 104 or 106?
• 106
• Which number is larger 10-4 or 10-6?
• 10-4
• think about it what is the larger number
• 1/10,000 or 1/1,000,000

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Acidic or basic

• H gt 10-7 solution is acidic
• H 10-7 solution is neutral
• H lt 10-7 solution is basic
• Or other way around
• OH- gt 10-7 solution is basic
• OH- 10-7 solution is neutral
• OH- lt 10-7 solution is acidic

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H/OH- concentrations in acids and bases

• H OH- H OH- H OH-
• acid neutral base

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Algebra

• Whats a logarithm?
• Writing exponents w/o superscript
• Example
• log 103 3
• log 10-3
• -3
• -log 10-3
• 3

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How much alkalinity/acidity

• Easier way of expressing acidity/alkalinity
• Focuses only on H concentration, called pH
  (little p, big H!!!)
• The pH of a solution is the negative logarithm of
  the hydrogen ion concentration
• pH -log H
• Artificial scale ranging from 0 to14

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Example H2O

• A few water molecules do this
• H2O ? H OH-
• Is water an acid or a base?
• How many molecules break up?
• 10-7
• Water has H 10-7
• pH -log 10-7
• pH 7
• Because water is considered neutral, pH 7 is the
  neutral pH

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pH of Household Liquids
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Addtl. definition of an acid/base

• Acid has a pH lt 7 (0 - 6.9)
• Base has a pH gt 7 (7.1 - 14)