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Acid/Base Strength

Acid/Base Strength. Strong and Weak Acids. Strong acids : completely ionize in aqueous solutions HCl (g) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) Weak acids : ionize slightly ion aqueous solutions CH 3 COOH (aq) + H 2 O (l) H 3 O + (aq) + CH 3 COO - (aq)

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Acid/Base Strength

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  1. Acid/Base Strength

  2. Strong and Weak Acids • Strong acids: completely ionize in aqueous solutions HCl (g) + H2O (l) H3O+(aq) + Cl-(aq) • Weak acids: ionize slightly ion aqueous solutions CH3COOH (aq) + H2O (l) H3O+(aq) + CH3COO-(aq) • Table on pg. 645 gives formulas for common weak acids

  3. Strong and Weak Acids • Another clue: the conjugate base! • Strong acids have WEAK conjugate bases • Weak acids have STRONG conjugate bases HCl (g) + H2O (l) H3O+(aq) + Cl-(aq) weak c.b. CH3COOH (aq) + H2O (l) H3O+(aq) + CH3COO-(aq) strong c.b.

  4. Acid Dissociation Constant (Ka) • For weak acids: Ka = [H3O+]coeff. x [A-]coeff. [HA]coeff. • Weak acids have small Ka values, strong acids have larger Kavalues. CH3COOH(l) + H2O(l) CH3COO-(aq) + H3O+(aq)

  5. Strong and Weak Bases • Strong bases: dissociate completely into metal ions and hydroxide ions in water NaOH (s) Na+(aq) + OH-(aq) • Weak bases: react with water to form a hydroxide ion and the conjugate acid of the base. NH3 (aq) + H2O (l) NH4+(aq) + OH-(aq)

  6. Base Dissociation Constant (Kb) • For dilute (weak) bases: Kb = [conjugate acid]coeff. x [OH-]coeff. [base]coeff. NH3 (aq) + H2O (l) NH4+(aq) + OH-(aq) • Weak bases have small Kb

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