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BrønstedLowry Theory

• Brønsted-Lowry Theory of Acids and Bases
• An acidbase reaction is a proton-transfer
  reaction in which
• the proton is transferred from the acid to the
  base.
• Acid
• A compound from which a proton can be removed.
• Base
• A compound that can remove a proton.

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BrønstedLowry Theory
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BrønstedLowry Theory
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BrønstedLowry Theory

• Amphoteric
• A substance that can behave as an acid
• in one situation and a base in another.
• Reversible Reaction
• The products of the reaction can react with
  themselves
• to reproduce the original reactants.
• Forward Direction Left to right
• Reverse Direction Right to left

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BrønstedLowry Theory
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BrønstedLowry Theory

• General equation for a BrønstedLowry
• proton-transfer reaction
• B HA HB
  A
• base acid
• proton proton
• remover source

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Lewis Theory

• Lewis Theory of Acids and Bases
• Acid
• Electron-pair acceptor.
• Base
• Electron-pair donor.

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Lewis Theory
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AcidBase Theories

• Summary of AcidBase Theories

Theory Acid Definition Base Definition
Historical Sour taste Bitter taste
Arrhenius More H than OH More OH than H
BrønstedLowry Proton source Proton remover
Lewis Electron-pair acceptor Electron-pair donor
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Conjugate AcidBase Pairs

• B HA HB
  A
• base acid
  acid base
• proton proton
  proton proton
• receiver source
  source receiver
• Conjugate AcidBase Pair
• Two species that transform into each other by
• gain or loss of a proton, H.
• Based on the Brønsted-Lowry theory.
• HB B and HA A are conjugate acidbase pairs

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Conjugate AcidBase Pairs
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Conjugate AcidBase Pairs
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Conjugate AcidBase Pairs

• Example
• What is the conjugate acid of NH3? What are the
  conjugate acid and conjugate base of HCO3?
• Solution
• To write the formula of a conjugate acid, add one
  H.
• To write the formula of a conjugate base,
  subtract one H.
• The conjugate acid of NH3 is NH4.
• The conjugate acid of HCO3 is H2CO3.
• The conjugate base of HCO3 is CO32.

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Acid/Base Relative Strengths

• In Chapter 9, we classified acids as strong or
  weak
• Strong acids were considered to be completely
  ionized
• HSt(aq) H(aq) St(aq)
• Weak acids were considered to be completely
  un-ionized
• HWk(aq)

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Acid/Base Relative Strengths

• Nitric acid is a stronger acid it is a good
  proton source.
• Consider the ionization equation for nitric acid
• HNO3(aq) H(aq) NO3(aq)
• The conjugate base of the acid is on the
• right-hand side of the equation.
• A base is a proton remover.

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Acid/Base Relative Strengths

• Hydrofluoric acid is a weaker acid it is a poor
  proton source.
• Consider the ionization equation for hydrofluoric
  acid
• HF(aq) H(aq) F(aq)
• The conjugate base of the acid is on the
• right-hand side of the equation.
• A base is a proton remover.

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Acid/Base Relative Strengths
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Predicting AcidBase Rxns

• Predicting the Favored Direction of a
• Proton-Transfer Reaction
• The stronger acid will always surrender a proton
• to the stronger base, yielding the weaker
• acid and base as favored species at equilibrium.

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Predicting AcidBase Rxns

• Procedure
• How to Predict the Favored Direction of
• an AcidBase Reaction
• For a given pair of reactants, write the equation
  for the transfer of one proton from one species
  to the other. (Do not transfer two protons.)
• Label the acid and base on each side of the
  equation.
• Determine which side of the equation has both the
  weaker acid and the weaker base (they must both
  be on the same side). That side identifies the
  products in the favored direction.

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Predicting AcidBase Rxns

• Example
• Write the net ionic equation for the reaction
  between hydrogen sulfate ion and hydroxide ion.
  Predict which side will be favored at
  equilibrium.
• Solution
• Step 1 For a given pair of reactants, write the
  equation for the transfer of one proton from one
  species to the other. (Do not transfer two
  protons.)
• HSO4(aq) OH(aq) SO42(aq) HOH(l)

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Predicting AcidBase Rxns

• Write the net ionic equation for the reaction
  between hydrogen sulfate ion and hydroxide ion.
  Predict which side will be favored at
  equilibrium.
• Step 2 Label the acid and base on each side of
  the equation.
• HSO4(aq) OH(aq) SO42(aq) HOH(l)
• Acid Base
  Base Acid

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Predicting AcidBase Rxns

• Write the net ionic equation for the reaction
  between hydrogen sulfate ion and hydroxide ion.
  Predict which side will be favored at
  equilibrium.
• Step 3 Determine which side of the equation has
  both the weaker acid and the weaker base (they
  must both be on the same side). That side
  identifies the products in the favored direction.
• HSO4(aq) OH(aq) SO42(aq) HOH(l)
• ? ?
  ? ?
• Acid Base
  Base Acid

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Predicting AcidBase Rxns
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Predicting AcidBase Rxns

• Write the net ionic equation for the reaction
  between hydrogen sulfate ion and hydroxide ion.
  Predict which side will be favored at
  equilibrium.
• From Table 17.1, HSO4(aq) is a stronger acid
  than HOH(l)
• SO42(aq) is a weaker base than OH(aq)
• HSO4(aq) OH(aq) SO42(aq) HOH(l)
• Stronger Stronger
  Weaker Weaker
• Acid Base
  Base Acid
• The reaction is favored in the forward direction.

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Predicting AcidBase Rxns
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The Water Equilibrium

• Autoionization of water

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The Water Equilibrium

• H2O(l) H(aq) OH(aq)
• Kw H OH 1.0 ? 1014
• Kw is the water constant or equilibrium constant
  for water
• If H OH x
• Kw H OH 1.0 ? 1014
• H OH 107 moles/liter

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The Water Equilibrium

• For water or water solutions
• If H OH 107 M,
• the solution is neutral.
• If H gt OH,
• the solution is acidic.
• If H lt OH,
• the solution is basic.

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The Water Equilibrium

• Example
• What is the hydrogen ion concentration in a
  solution in which the hydroxide ion concentration
  is 104 M? Is the solution acidic or basic?
• Solution
• GIVEN OH 104 M WANTED H
• EQUATION Kw H OH 1.0 ? 1014
• H 1010 M
• Since H 1010 lt OH 104, the solution
  is basic

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pH and pOH (Integer Values)

• A mathematical function is a rule
• that describes how to change one quantity to
  another.
• The p function
• pQ log Q
• Applied to H and OH,
• pH log H
• pOH log OH

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pH and pOH (Integer Values)

• Inverse Functions
• pH log H
• pH log H
• antilog (pH) antilog (log H)
• antilog (pH) H
• Similarly,
• OH antilog (pOH)

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pH and pOH (Integer Values)

• Example
• What is the pH of a solution with H 105 M?
  What is the OH of a solution with pOH 6?
• Solution
• pH log H log 105 5
• OH antilog (pOH) antilog (6) 106 M

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pH and pOH (Integer Values)

• Kw H OH 1.0 ? 1014
• H OH 1.0 ? 1014
• log (H OH) log (1.0 ? 1014)
• log (H OH) 14
• log H ( log OH) 14
• pH pOH 14

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pH and pOH (Integer Values)

• Example
• The hydrogen ion concentration of a solution is
  103 M. What are the pH, pOH, and OH of the
  solution?
• Solution
• pH log H log 103 3
• pH pOH 14
• pOH 14 pH 14 3 11
• OH antilog (pOH) antilog (11) 1011 M

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pH and pOH (Integer Values)

• A solution is neutral if H 107 M
• A solution is acidic if H gt 107 M
• A solution is basic if H lt 107 M
• Using pH log H and pOH log OH,
• A solution is neutral if pH 7
• A solution is acidic if pH lt 7
• A solution is basic if pH gt 7

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pH and pOH (integer Values)
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pH and pOH (integer Values)
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Noninteger pH-H/pOH-OH

• Significant Figures and Logarithms
• In a logarithm, the digits to the left of the
  decimal are not counted as significant figures.
  Counting significant figures in a logarithm
  begins at the decimal point.

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Noninteger pH-H/pOH-OH
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Noninteger pH-H/pOH-OH

• Example
• The hydrogen ion concentration of a solution is
  2.7 ? 106 M. What are the pH, pOH, and hydroxide
  ion concentration?
• Solution
• pH log H log (2.7 ? 106) 5.57
• pH pOH 14.00
• pOH 14.00 pH 14.00 5.57 8.43
• OH antilog (pOH) antilog (8.43) 3.7 ?
  109 M