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Strength of Acids and Bases

Strength of Acids and Bases. Electrical Conductivity. Acidic and basic solutions conduct electricity. Strengths of Acids. Acids that completely ionize (dissociate) are called strong acids. Strong acids produce a strong electric current = strong electrolyte

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Strength of Acids and Bases

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  1. Strength of Acids and Bases

  2. Electrical Conductivity • Acidic and basic solutions conduct electricity.

  3. Strengths of Acids • Acids that completely ionize (dissociate) are called strong acids. • Strong acids produce a strong electric current = strong electrolyte • HCl(aq) +H2O(l)  H3O+(aq) + Cl-(aq)

  4. Strengths of Acids • Weak acids partially ionize in solutions = weak electrolyte • Produce fewer ions and cannot conduct electricity as efficiently as strong acids • HC2H3O2(aq) +H2O(l)  H3O+(aq) + C2H3O2−(aq)

  5. Six Strong Acids • Hydrochloric acid: HCl  • Hydrobromic acid: HBr  • Hydroiodic acid: HI  • Sulfuric acid: H2SO4 • Nitric acid: HNO3 • Perchloric acid: HClO4 These acids completely dissociate in water.

  6. Strength of Bases • Strong bases dissociate entirely into metal ions and hydroxide ions. • Weak bases ionizes only partially in dilute aqueous solution

  7. Eight Strong Bases • Lithium hydroxide: LiOH  • Sodium hydroxide: NaOH  • Potassium hydroxide: KOH  • Rubidium hydroxide: RbOH  • Cesium hydroxide: CsOH  • Calcium hydroxide: Ca(OH)2 • Strontium hydroxide: Sr(OH)2 • Barium hydroxide: Ba(OH)2 These bases completely dissociate in water. 

  8. Acid/Base Strength vs. Concentration • Do not get acid/base strength confused with concentration. • Acid/base strength is based on the ability to dissociate. • Concentration is based on how much is dissolved in solution. • You can have a strong dilute acid – the acid completely dissociates, but there is not much acid dissolved in solution

  9. Acid Ionization Constant • Acid ionization constant (Ka) is the value of the equilibrium constant expression(Keq) for the ionization of a weak acid. • Large Ka strong acid • Small Ka weak acid

  10. Base Ionization Constant • The base ionization constant (Kb) is the value of the equilibrium constant expression (Keq) for the ionization of a base • Large Kb strong base • Small Kb weak base

  11. Write the ionization equation and acid ionization constant (Ka) expressions for the acid HF If you calculate Ka, it will be a weak acid so it will have a double arrow. Add it to water. HF + H2O(l)  H3O+ + F- (A) (B) (CA) (CB) Ka = [H3O+ ] × [F-] [HF] Leave out liquids and solids in Keq

  12. Write the ionization equation and base ionization constant (Kb) expressions for the base NH3 If you calculate Kb, it will be a weak base so it will have a double arrow. Add it to water. NH3 + H2O(l)  NH4+ + OH- (B) (A) (CA) (CB) Kb = [NH4 + ] × [OH-] [NH3] Leave out liquids and solids in Keq

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