4.6%20Acids%20and%20Bases:%20General%20Principles

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4.6Acids and Bases General Principles
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4.6Acids and Bases General Principles

• Brønsted-Lowry definitionan acid is a proton
  donora base is a proton acceptor

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Proton Transfer from HBr to Water
hydronium ion

• base acid conjugate conjugate acid base

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Acid Strength

• A strong acid is one that is completely ionized
  in water.
• A weak acid is one that ionizes in water to the
  extent of less than 100.
• Acid strength is measured by Ka or pKa

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Equilibrium constant for proton transfer
..

.
.

O

Br
H
H
O
..
H3OBr
K
HBr
HBr
K a
HBr
pK a log Ka
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Table 4.2 Strength of Some Brønsted Acids

• strong acids are stronger than hydronium ion

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Table 4.2 Strength of Some Brønsted Acids

• weak acids are weaker than hydronium ion

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Table 4.2 Strength of Some Brønsted Acids

• alcohols resemble water in acidity their
  conjugatebases are comparable to hydroxide ion
  in basicity

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Table 4.2 Strength of Some Brønsted Acids

• ammonia and amines are very weak acidstheir
  conjugate bases are very strong bases

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Proton Transfer to Alcohols
alkyloxonium ion

• base acid conjugate conjugate acid base

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4.7Acid-Base ReactionsA Mechanism for Proton
Transfer
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Proton Transfer from HBr to Water

• base acid conjugate conjugate acid base

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Mechanism single step

transition state
Potentialenergy
activation energy
reactants
products

Reaction coordinate
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Mechanism single step

d
d-

• bimolecularboth H2O and HBr involved at
  transition state

Potentialenergy
H2O HBr

Reaction coordinate