CHAPTER 16: (HOLT) ACID-BASE TITRATION AND pH

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CHAPTER 16 (HOLT)ACID-BASE TITRATION AND pH
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I. Concentration Units for Acids and Bases

• A. Chemical Equivalents
• 1. Definition quantities of solutes that
  have equivalent combining capacity
• a. Acid mass of one equivalent is
  numerically equal to the mass of one mole of the
  acid divided by the number of protons(H or H3O
  ) that one mole of the acid can provide
• Example
• HCl 36 g/mol 1 eq 1H 36
  g/mol H
• H2SO4 98g/mol 2 eq 2H 49
  g/mol H

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• B. Base mass of one equivalent is numerically
  equal to the mass of one mole of the base divided
  by the number of protons(OH-) that one mole of
  the base can provide
• Example
• NaOH 40 g/mol 1 eq 1 OH- 40 g/mol
  OH-
• Ca(OH)2 74 g/mol 2 eq 2 OH- 37 g/mol
  OH-

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B. Normality

• Definition number of equivalents of solute per
  liter of solution
• N eq of solute
• L of solution

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C. Relationship Between Normality and Molarity

• N nM
• N Normality
• n number of equivalents ( of H or OH-)
• M Molarity
• Example
• 1M HCl 1N HCl 1M NaOH 1N
  NaOH
• 1M H2SO4 2N H2SO4 1M Ca(OH)2 2N
  Ca(OH)2

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II. Aqueous Solutions and the Concept of pH

• A. Self-Ionization of Water
• 1. Definition Two water molecules interact
  to produce a hydronium ion and a hydroxide ion by
  proton transfer - forms a weak electrolyte
• 2. is symbol used to indicate
  concentration in moles per liter (Molarity)
• 3. H2O H2O lt---gt H3O OH-
• in pure water H3O OH-
• 4. H3O OH- 10-14
• 5. If the H3O increases then the OH-
  decreases or
• If the H3O decreases then the OH-
  increases

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B. The pH scale

• 1. pH -- the negative of the common logarithm of
  the hydronium ion concentration
• pH -logH3O
• 2. Acid pH lt 7
• 3. Base pH gt 7
• 4. Neutral pH 7

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C. Calculations involving pH

• pH -logH3O
• 0.001 M HCl H3O 1 x 10 -3
• pH -log1 x 10-3
• pH 3 (acid)
• Remember that H3O OH- 1 x 10-14 so
  if H3O 1 x 10-3 then OH- 1 x 10-11
• FYI there is also pOH - logOH- and
• pH pOH 14

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III. Acid-Base Titrations

• A. Indicators
• 1. Definitions
• a. indicators - weak acid or base dyes
  whose colors are sensitive to pH, or hydronium,
  concentration
• b. transition interval - the pH range
  over which an indicator changes color

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• 2. Types of indicators
• a. Change color at about pH 7
• b. Change color below pH 7
• c. Change color above pH 7

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B. The Principle of Titration

• Definitions
• 1. Titration - the controlled addition and
  measurement of the amount of a solution of known
  concentration that is required to react
  completely with a measured amount of a solution
  of unknown concentration
• 2.Standard solution - a solution that
  contains a precisely known concentration of a
  solute

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• 3. Equivalence point - in a neutralization
  reaction, the point at which there are equivalent
  quantities of hydronium and hydroxide ions
• 4. End point - the point in a titration where an
  indicator changes color
• 5. Primary standard - a highly purified compound,
  when used in solution to check the concentration
  of the known solution in a titration

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C. Molarity and Titration

• 1. Determine the moles of acid (or base) from the
  standard solution used during titration
• 2. From a balanced chemical equation, determine
  the ratio of moles of acid (base) to base (acid)
• 3. Determine the moles of solute of the unknown
  solution used during the titration
• 4. Determine the molarity of the unknown solution

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D. Normality and Titrations

• Va x Na Vb x Nb
• Va volume of the acid
• Na normality of the acid
• Vb volume of the base
• Nb normality of the base