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Acids & Bases

Acids & Bases. Calculating Ka from % Dissociation Polyprotic Acids Properties of Salts. Example. Lactic acid (HC 3 H 5 O 3 ) is a waste product that accumulates in the muscle during exertion, leading to pain & a feeling of fatigue. A 0.100 M solution is 3.7% dissociated. Calculate K a.

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Acids & Bases

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  1. Acids & Bases Calculating Ka from % Dissociation Polyprotic Acids Properties of Salts

  2. Example • Lactic acid (HC3H5O3) is a waste product that accumulates in the muscle during exertion, leading to pain & a feeling of fatigue. A 0.100 M solution is 3.7% dissociated. Calculate Ka.

  3. Example HC3H5O3  H+ + C3H5O3-

  4. Polyprotic Acids • More that one ionizable H+ • H+ come off one at a time • Each one has a specific Ka value • Ka1>>>>Ka2>>Ka3 • When calculating the pH of a polyprotic acid, you only use the 1st Ka because all of the others are so small

  5. Complete Ionization • Write the steps for the complete ionization of H2Se

  6. Complete Ionization • Write the steps for the complete ionization of H3AsO

  7. Example • Calculate the pH & the [ ] of all species of a 3.0 M solution of H3PO4. • Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8, Ka3 = 4.8 x 10 -13

  8. Example H3PO4 H+ + H2PO4- Ka1 = 7.5 x 10-3

  9. Example H2PO4 - H+ + HPO4-2 Ka1 = 6.2 x 10-8

  10. Example HPO4 -2 H+ + PO4-3 Ka3 = 4.8 x 10-13

  11. Example • pH = • [H3PO4] = • [H2PO4-] = • [HPO4-2] = • [PO4-3] = • [H+] =

  12. Acid Base Properties of Salts • Salts of weak acids produce basic solutions • NaC2H3O2

  13. Acid Base Properties of Salts • Salts of weak bases produce acidic solutions • NH4Cl

  14. Acid Base Properties of Salts • Salts of strong acids & Bases produce neutral solutions • NaCl

  15. Calculations with salts • KaxKb = Kw • Can find Ka or Kb with this equation • On AP formula sheet

  16. Example • What is the pH if a 0.140M solution of NaC2H3O2 (KaHC2H3O2 = 1.8x10-5)

  17. Another example • What is the pH of a 0.140M solution of diethylaminochloride (C2H5)2NH3Cl. • Kb (C2H5)2NH3+ = 1.3x10-3 • (C2H5)2NH3Cl  (C2H5)2NH3+ + Cl- • (C2H5)2NH3+ + H2O  (C2H5)2NH2 + H3O +

  18. Qualitative Predictions of pH • Ka>Kb  acidic • Kb>Ka  basic • Ka = Kb  neutral

  19. pH Predictions • Predict if an aqueous solution of the following are acidic, basic, or neutral • NH4C2H3O2 • Kb NH4+ = 1.8x10-5 • Ka HC2H3O2 = 1.8x10-5

  20. pH Predictions • Predict if an aqueous solution of the following are acidic, basic, or neutral • NH4CN • Kb NH4+ = 1.8x10-5 • Ka HCN= 6.2x10-10

  21. Effect of Structure of Acid Base Properties • Weak acid (HF) • Stays together • Strong acids • Look at electronegativity

  22. Effect of Structure of Acid Base Properties

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