1. Chapter 14 Acids and Bases
14.4 Dissociation Constants for Acids and Bases
Learning Goal Write the expression for the dissociation constant of a weak acid or weak base.
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2. dissociate completely in water, producing high concentrations of ions
Strong Acids and Bases
Strong acids and bases
dissociate completely in water, producing high concentrations of ions
HCl(aq) + H2O(l)  H3O+(aq) + Cl−(aq)
NaOH(aq)  Na+(aq) + OH−(aq)
have very large dissociation constants that are not usually given
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3. Weak Acids, Dissociation Constants
Weak acids and bases
produce small amounts of ions in water
HCHO2(aq) + H2O(l) H3O+(aq) + CHO2−(aq)
partially dissociate in water and have a dissociation constant
The acid dissociation constant for HCHO2 is: ×
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4. Weak Bases, Dissociation Constant
Weak bases also have a dissociation constant, called the base dissociation constant, Kb.
CH3NH2(aq) + H2O(l) CH3NH3+(aq) + OH−(aq) ×
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5. Ka, Kb Strength of Weak Acids, Bases
The larger the Ka, Kb value for an acid or base,
the larger the ratio of products to reactants
the larger the concentration of ions produced
the stronger the acid or base
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6. Ka, Kb Weak Acids and Bases
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7. Characteristics, Acids and Bases
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8. Learning Check
Write the equilibrium reaction and dissociation constant for the weak acid, HCN.
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9. HCN(aq) + H2O(l) H3O+(aq) + CN−(aq)
Solution
Write the equilibrium reaction and dissociation constant for the weak acid, HCN.
HCN(aq) + H2O(l) H3O+(aq) + CN−(aq)
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10. Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2.
Learning Check
Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2.
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11. Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2.
Solution
Write the equilibrium reaction and Kb for the weak base CH3—CH2 –NH2.
CH3—CH2 –NH2(aq) + H2O(l)
OH−(aq) + CH3—CH2 –NH3+(aq)
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