Acid and Base Equilibrium

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Acid and Base Equilibrium

• CHM1025C

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Arrhenius

• Acid A substance that make H (H3O) when
  dissolved in water.
• Base A substance that makes OH- when dissolved
  in water.
• An acid/base reaction occurs when and H from an
  acid reacts with an OH- from a base.

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Acids

• Strong acids Dissociate completely when
  dissolved in water.
• HCl, HNO3
• Weak acids only dissociate a little bit.
• CH3CO2H

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Base

• Strong base dissociates completely when
  dissolved in water.
• NaOH, KOH
• Weak base Makes only a little bit of OH-
• NH3

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Electrolyte

• Electrolyte A substance that produces ions when
  dissolved in water.
• NaCl, HCl and NaOH are all strong electrolytes
  because they dissociate essentially completely
  into ions. Strong acids and strong bases are
  strong electrolytes.
• CH3CO2H, HF and NH3 are examples of weak
  electrolytes because they produce only a few ions.

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1.00 M Acetic acid, a weak acid

• CH3COOH (aq) H2O(l) ? H3O(aq) CH3COO-(aq)
• The Ka for this reaction is 1.8 x 10-5. Since
  little of the CH3CO2H dissociates, we can call it
  1 M.
• For every H3O there will be one CH3COO-. Let
  these concentrations x
• xH CH3COO- .00042

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Brønsted-Lowry Definition

• Acid A proton donor.
• Base A proton acceptor.
• An acid base reaction is one where there is a
  proton transfer.
• A broader definition than the Arrhenius
  definition.
• conjugate base The acid without an H.
• conjugate acid The base with an H.

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TABLE Relative Strengths of Acids and Their
Conjugate Bases
Given on test
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A standard acid/base reaction
Acid Base ? c. base c. acid
CH3COOH H2O ? CH3COO- H3O
ex
NH3 H2O? NH4 OH-
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More on Acid Base reactions

• Water is amphoteric or amphiprotic, it can act as
  both an acid and a base.
• All acid base reactions are equilibrium reactions
• The equilibrium lies to the side of the weaker
  acid.
• When the equilibrium lies to the right, a lot of
  reaction occurs and there is often heat released
  or there is a color change.
• When the equilibrium lies to the left very little
  reaction occurs. (no heat)

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Water

• Water auto-ionizes
• H2O H2O ? H3O OH-
• acid base
  10-7M 10-7M

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Acids and pH
0.1 M HCl pure water 0.1 M NaOH
H or H3O 0.100 or 1.00 x10-1 1x10-7 1.00 x10-13
OH- 1.00 x10-13 1x10-7 0.100 or 1.00 x10-1
pH 1 7 13
pOH 13 7 1
acid or basic Acid H3OgtOH- neutral H3OOH- Basic H3OltOH-
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pH scale
Lemon juice Soda vinegar
ammonia Comet cleanser drano
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The big six

1. H3O OH- 1 x 10-14
2. pH -logH3O
3. pOH -logOH-
4. H3O 10-pH
5. OH-10-pOH
6. pH pOH 14

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The H or H3O of 0.1 M NH3

• The pH is 11.13. What is the H3O ?
• pH -log H3O
• H3O 10-pH
• H3O 10-11.137.41 x 10-12

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Filling out a table
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Buffer solution

• A buffer solution keeps the pH approximately the
  same even upon the addition of a strong acid or
  strong base.
• Need a weak acid.
• Its conjugate base.
• Present in a large enough quantity to resist the
  pH changes.

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CH3CO2H/CH3CO2-

• If you add an acid, H, The base of the buffer
  reacts.
• H CH3CO2- ? CH3CO2H
• H3O CH3CO2- ? H2O CH3CO2H
• Of you add a base, OH-, the acid of the buffer
  system reacts.
• CH3CO2H OH- ? H2O CH3CO2-

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Titrations

• How many mL of 0.660M H2SO4 are required to react
  completely with 72.5 mL of 0.137M NaOH?