Acids/Bases

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Acids/Bases

• Svante Arrhenius, a Swedish chemist, proposed the
  following definition
• Acids form hydronium ions in aqueous solutions,
  while bases form hydroxide ions.
• Acids give off H
• Bases give off OH-

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Properties of acids

• Give foods a tart or sour taste
• Electrolytes
• React with hydroxide ions to form water and a
  salt
• HCl NaOH --gt NaCl H2O

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Properties of bases

• React with acids to form water and salt
• Have a bitter taste
• Have a slippery feel
• Electrolytes
• Milk of Magnesia (Magnesium Hydroxide) is a base
  used to treat excess stomach acid problems.

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Hydrogen Ions from WaterThis is the basis to
start understanding pH

• Water is considered neutral
• Collision between water molecules can cause a
  hydrogen ion to transfer from one molecule to
  another.
• H2O H2O H3O
  OH-
• hydronium ion hydroxide
  ion

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Self-Ionization of Water
Water self ionizes to the concentration of 1.0 x
10-7 mol/L. When the concentration of each ion
equals 1.0 x 10-7 mol/L the solution is said to
be neutral Therefore, since water is considered
neutral the concentrations of the ions can be
calculated through the Ion product constant.
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The Ion-Product ConstantKw

• Notation
• H - concentration of hydrogen ions
• Or hydronium ions
• OH- - concentration of hydroxide ions
• When H and OH- are multiplied we get the
  ion-product constant.
• Kw H x OH- 1.0 x 10-14 (mol/L)2 or M2
• This is an inverse relationship.
• One goes up, the other goes down.

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The Ion-Product ConstantKw example problem

• If H 1.0 x 10-5 mol/L, is the solution
  acidic, basic, or neutral? What is the OH- of
  this solution?
• Answer
• Acidic - the H is greater than 1.0 x 10-7
  mol/L
• 1.0 x 10-5 mol/L x OH- 1.0 x 10-14 M2
• OH- 1.0 x 10-9 mol/L

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The Ion-Product ConstantKw example problem

• If OH- 2.8 x 10-8 mol/L, is the solution
  acidic, basic, or neutral? What is the H of
  this solution?
• Answer
• acidic - the OH- is less than 1.0 x 10-7 mol/L
• H x 2.8 x 10-8 mol/L 1.0 x 10-14 M2
• H 3.5 x 10-7 mol/L