Understanding Strong and Weak Acids and Bases in Aqueous Solutions
This guide explains the key differences between strong and weak acids and bases. Strong acids, like HCl, fully ionize in water, while weak acids, such as acetic acid (CH3COOH), only partially ionize. The nature of their conjugate bases is also crucial: strong acids correspond to weak conjugate bases, and weak acids correspond to strong conjugate bases. The Acid and Base Dissociation Constants (Ka and Kb) further illustrate these differences, showing that weak acids and bases have smaller dissociation constants compared to their strong counterparts.
Understanding Strong and Weak Acids and Bases in Aqueous Solutions
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Presentation Transcript
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
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.
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)
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)
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
