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Acids / Bases

Acids / Bases. Strong Completely dissociate into ions Large increase in [ H + ] or [ OH - ] To determine if strong: Check list/memory When comparing two binary acids ( H+nonmetal ) , strength increases as the size of the nonmetallic atom icreases (EX: HBr > HCl )

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Acids / Bases

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  1. Acids/Bases Strong • Completely dissociate into ions • Large increase in [H+] or [OH-] • To determine if strong: • Check list/memory • When comparing two binary acids (H+nonmetal) , strength increases as the size of the nonmetallic atom icreases (EX: HBr > HCl) • When comparing oxyacids (H+polyatomic ion), the one with the larger # of oxygens is stronger OR the greater the electronegativity of the nonmetal atom the stronger the acid (EX: HNO3 > HNO2; HNO3 > HBrO3)

  2. weak • Partially ionize when placed in water • Establishes equilibrium • Almost ALL acids encountered will be weak • HA  H+ + A-Ka = [H+][A- ] [HA] **A list of known Ka values are in appendix D (pg. 1022) of your textbook. **A greater value for Ka the stronger the acid HF - Ka = 7.2 x 10-4 > HCN - Ka = 6.2 x 10-10 When calculating equilibrium concentrations, use the stronger acid b/c it’s the one that supplies the greater # of ions thus affecting the acidity the most

  3. Calculate the pH of a 0.10 M HNO3 solution. • Calculate the pH of a 0.10 M HOCl solution.

  4. Polyprotic Acids • Acids that contain more than 1 H • The H’s dissociate one at a time, each step having its own Ka value • Ka1 > Ka2 > Ka3 ; this tells us that the acid gradually becomes weaker with the loss of each H • When calculating pH, we only have to use the first dissociation since it’s the strongest acid

  5. Calculate the pH and the equilibrium concentrations of H3PO4, H2PO4-, HPO4-2, and PO4-3 for a 5.0 M H3PO4 solution.

  6. Mixture of Acids Calculate the pH of a solution that contains 1.00 M HCN and 5.00 M HNO2

  7. Weak Bases • Partially ionize in water, establishing equilibrium • Most contain OH-, but weak bases typically combine with water to produce OH- • Use Bronsted-Lowry to determine the base NH3 + H2O  NH4+ + OH- Kb = [NH4+][OH-] [NH3] **A list of Kb values are found in appendix D of your textbook ** A larger Kb value indicates a stronger base **Kw = Ka(Kb)

  8. Calculate the pH of a 15.0 M NH3 solution.

  9. % dissociation/ionization • Tells how much of the weak substance has dissociated/ionized • % = amount dissociated/ionized * 100 initial concentration

  10. Calculate the percent dissociation of a 1.00 M acetic acid solution.

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