SUMMMARY

Acids and Bases

Acid Strength

Strong Acids

·Completely dissociate (ionize)

·Have weak conjugate bases

·HCl, HBr, HI, H₂SO₄, HNO₃, HClO₄, HClO₃

Weak Acids

·Do not completely ionize

·Have a strong conjugate base

·CH₃COOH

Water as an Acid and a Base

Amphoteric Substances

·Behave like acids and bases

·H₂O, NH₃, HSO₄^–

Ionization of Water

H₂O     +     H₂O   →           H₃O⁺ +      OH^–

Hydronium Ion

Ionization of Water simplified

H₂O    →    H⁺ +    OH^–

At 25°C, [H⁺]  =  [OH^–]   =   1.0 x 10^-7 moles / L

[H⁺] x [OH^–]   =   1.0 x 10^-14 = K_w

In a neutral solution,   [H⁺] = [OH^–]            (pH = pOH)

In an acidic solution,   [H⁺] > [OH^–]            (pH < 7.0)

In a basic solution,      [H⁺] < [OH^–]            (pH > 7.0)

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The pH Scale

pH = – log [H⁺]

pOH = – log [OH^–]

pH + pOH = 14

In a neutral solution,  pH = pOH

In a basic solution,     pH > pOH   Note: the higher the [H⁺], the lower the pH

In an acidic solution,  pH < pOH      e.g. [H⁺]   = 1 x 10^-6,   pH   = 6

[OH^–] = 1 x 10^-8,  pOH = 8

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Buffers

A buffer is a solution is a solution of a weak acid and its conjugate base.

e.g. 0.1 M acetic acid and 0.1 M sodium acetate

A buffer resists pH change.

Recall the weak acid acetic acid is largely unionized:

CH₃COOH + H₂O   →     CH₃COO^– +   H₃O⁺

95%                                                  5%

Adding strong OH^– or H⁺ produces almost no pH change because they react with the conjugate acid or base, respectively.

See:

http://www.wwnorton.com/college/chemistry/chemistry3/ch/17/chemtours.aspx

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Acid Base Ionization

http://cdn.wwnorton.com/college/chemistry/chem3/chemtours/chapter_17/acid_base_ionization/Interface.swf

Self-ionization of Water:

http://cdn.wwnorton.com/college/chemistry/chem3/chemtours/chapter_17/self_ionization/Interface.swf

Note: An excellent animation of the relative strength of acids is found at:

Acid Strength and Molecular Structure

http://media.wwnorton.com/college/chemistry/chemtours/chapter_17/acid_strength/interface.swf

Additional animations:

pH Scale

http://media.wwnorton.com/college/chemistry/chemtours/chapter_17/ph_scale/interface.swf

Acid/Base Titrations

http://media.wwnorton.com/college/chemistry/chemtours/chapter_17/strong_titrations/interface.swf

Buffers

http://media.wwnorton.com/college/chemistry/chemtours/chapter_17/buffers/interface.swf

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A good review of the inductive effect of electronegativity on relative acid strengths can be found at:

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http://en.wikipedia.org/wiki/Acids