Lecture 51 Acids and Bases I

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Lecture 51 Acids and Bases I
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Acids and Bases

• the acid test
• acid drop
• acid rain
• put the acid on
• do acid, acid head

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Acids and Bases

• Acids
• taste sour
• Bases (Alkalis)
• taste bitter, feel slippery

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Acids and Bases

• Everyday examples
• Acids
• battery acid, many foods, Aspirin, wine
• Bases
• Drano, Fantastik, ammonia, baking soda, blood

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The Three Gurus of Acids and Bases

• 1. Svante Arrhenius (1887)
• Acid Water H(aq) X-(aq)
• (Ionization of the acid)
• Base Water X(aq) OH-(aq)
• (Ionization of the base)

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The Three Gurus of Acids and Bases

• 1. Svante Arrhenius (1887)
• problems
• - only works in aqueous solutions
• - only works for one kind of base
• (OH- - containing)

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The Three Gurus of Acids and Bases

• 2. Johannes Brônsted,
• Thomas Lowry (1923)
• Acids donate protons
• Bases accept protons

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Bronsted-Lowry Theory
HA

B
BH

A-
¾
acid
conjugate base of HA
base
conjugate acid of B
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Water Can be an Acid or a Base...

• HCl(aq) H2O(l) ¾ H3O(aq) Cl-(aq)
• NH3(aq) H2O ¾ OH-(aq) NH4(aq)

acid
base
acid
base
base
acid
base
acid
H3O(aq) the Hydronium ion
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or both !

• H2O(l) ¾ H(aq) OH-(aq)
• or, H2O(l) H2O(l) ¾ H3O(aq) OH-(aq)

water is amphoteric
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The Three Gurus of Acids and Bases

• 3. G.N. Lewis
• An acid accepts an electron pair
• A base donates an electron pair

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Lewis Bases have at least one lone pair

• e.g. H2O

?
OH-

conjugate acid of H2O
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Lewis Bases have at least one lone pair

• e.g. OH-

H
-
..
..

O
O - H

? 2
..
..
H
conjugate acid of OH-
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Other Lewis Bases
..
-
Cl
..
(NH4)
(HCl)
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Strengths of Acids and Bases

• Strong Acid
• HA H2O ? H3O A-
• (complete dissociation)
• Weak Acid
• HA H2O ¾ H3O A-
• (incomplete dissociation)

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Strengths of Acids and Bases

• In an acid-base reaction, the proton is
  transferred to the stronger base

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Strengths of Acids and Bases

• HCl(aq) H2O(l) ? H3O(aq) Cl-(aq)

HCl is a Strong Acid
H
i.e. H2O is a stronger base than Cl-
Strong acids have weak conjugate bases
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Strengths of Acids and Bases
Acetic acid is a Weak Acid

• CH3COOH(aq) H2O(l) ¾ H3O(aq) CH3COO-(aq)

H
i.e. CH3COO- is a stronger base than H2O
Weak acids have strong conjugate bases
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Acid Strength and Concentration

• ...are not the same thing
• e.g. 1.0 M HCl and 1.0 M H2CO3

stronger acid
same concentrations!
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Strengths of Acids and Bases
HClO4
ClO4-
HNO3
NO3-
F-
HF
stronger base
stronger acid
H2CO3
HCO3-
OH-
H2O
NH3
NH2-
O-2
OH-
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Naming Acids and Bases

• Acid Water ¾ H(aq) X-(aq)
• Acid Name Anion Name
• HCl hydrochloric chloride
• HClO hypochlorous hypochlorite
• HClO2 chlorous chlorite
• HClO3 chloric chlorate
• HClO4 perchloric perchlorate

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Naming Acids and Bases

• NaOH sodium hydroxide
• Ca(OH)2 calcium hydroxide
• NH3 ammonia
• H2O water (also an acid!)