Chemistry 12 Unit 4

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Chemistry 12 Unit 4
Chapter 20
Acid Base Equilibrium
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Unit IV Acid/Base Equilibrium
Introduction (Post Lab Discussion)
Operational Definitions

• Describe what acids or bases do

eg
Bases turn red litmus blue
eg
Acids react with magnesium
Conceptual Definitions

• Define acids or bases in terms of their molecular
  structure

eg
Acids contain H
eg
Bases contain OH-
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Arrhenius Definitions (Classic)
Acid
A substance that produces H in solution.
Base
A substance that produces OH- in solution.
Classic Neutralization Reaction
H2SO4(aq) 2 NaOH(aq) ? 2 H2O(l)
Na2SO4(aq)
Acid Base Water
Salt
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• Characteristics

Acids

• Sour taste

• React with metals (producing H2)

• Conduct electricity

Bases

• Bitter taste

• Feel slippery (soapy)

• Conduct electricity

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• Definitions (Bronsted / Lowry)

• Acid

Any substance that can dissociate or donate a
hydrogen ion (H or proton).
HCl ? H Cl-
eg
H2SO4 ? H HSO4-
eg
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• Base

Any substance that can accept a proton.
OH- H ? H2O
eg
(any substance containing hydroxide ion can act
as a base)
NaOH(s) ? Na(aq) OH-(aq)
eg
then if H is present.
OH-(aq) H(aq) ? H2O(l)
Some bases do not contain OH-
NH3(aq) H(aq) ? NH4(aq)
eg
Ammonia Ammonium ion

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• Amphiprotic substance

A substance that can act as either an acid or a
base depending on the situation.
H2O(l) HCl(aq) ? H3O(aq) Cl-(aq)
eg
Hydronium ion
(water is acting as a base)
H2O(l) NH3(aq) ? OH-(aq) NH4(aq)
eg
(water is acting as an acid)
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• Conjugate acid/base pairs

Two substances that differ by only one proton.
NH3 H2O ? OH- NH4
eg
Base
Base
Acid
Acid

• NH3 and NH4 are a conjugate acid/base pair and
  H2O and OH- are a conjugate acid/base pair.

(the substance with the extra proton is always
the conjugate acid)
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• A Bronsted/Lowry acid base reaction always
  consists of two conjugate acid base pairs

Other examples of C.A.B.P.s
eg

• H2O and H3O

• H2SO4 and HSO4-

• NH3 and NH2-

• Note in reality NH3 is a base, however it is
  the conjugate acid of NH2-.

• Note in reality H2O is a neither an acid nor a
  base, however it is the conjugate base of H3O.

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• Polyprotic substance

An acid or a base capable of donating or
accepting more than one proton.
H3PO4 is a polyprotic acid
eg
H3PO4 ? H H2PO4-
H2PO4- ? H HPO42-
HPO42- ? H PO43-
(specifically, H3PO4 is a triprotic acid.)