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Buffer Solutions, Function

Buffer Solutions, Function. HCl is added to pure water. OWL - 18.2a. HCl is added to a solution of a weak acid H 2 PO 4 - and its conjugate base HPO 4 2-. Simplified >. OWL - 18.2d. HOAc + H 2 O H 3 O + + OAc -. HOAc H + + OAc -. Simplified >.

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Buffer Solutions, Function

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  1. Buffer Solutions, Function HCl is added to pure water. OWL - 18.2a HCl is added to a solution of a weak acid H2PO4- and its conjugate base HPO42-.

  2. Simplified > OWL - 18.2d

  3. HOAc + H2O H3O+ + OAc- HOAc H+ + OAc- Simplified > The Metal Cation is not shown OAc-: CH3COO-

  4. HOAc H+ + OAc- OWL – 18.2c

  5. Preparing a Buffer You want to buffer a solution at pH = 4.30 [H3O+] = 5.0 x 10-5 M Best choice is…? What are the pKas? What are the molarities of HA, A-?

  6. Use pH = pKa + log[A-] [HA] pH = 4.74 + log(0.1/0.1) = 4.74 OWL – 18.2e, f, g, h, I, m

  7. Titration An analytical technique to determine the number of moles of a substance • Two Reactants: the ID of both are known but the moles of one are not known • One of many reactions 1. Acid/Base 2. Redox 3. Precipitation • One reactant in a flask the other reactant in a buret

  8. Acid-Base Titrations OWL 18.3a Adding NaOH from the buret to acetic acid in the flask, a weak acid. (In the beginning the pH increases very slowly.) Additional NaOH is added. pH rises as equivalence point is approached. Additional NaOH is added. pH increases and then levels off as NaOH is added beyond the equivalence point.

  9. Titrations

  10. OWL - 18.3e, c

  11. Know how to use the following terms: • Equivalence point • Buffer region OWL 18.3f, g

  12. Know how to select the appropriate indicator for an acid/base titration OWL 18.3h

  13. 18.4 • Know that Ksp is the equilibrium constant for precipitates • Know how to determine Ksp • Know how to calculate the solubility of precipitates using Ksp • Know how to calculate the solubility of precipitates considering the common ion effect • Know the effect of acids and bases on the solubility of precipitates

  14. Lead(II) Chloride PbCl2(s) Pb2+(aq) + 2 Cl-(aq) Ksp = 1.9 x 10-5 = [Pb2+][Cl–]2 OWL – 18.5b

  15. Some Values of Ksp Table 18.2 and Appendix J OWL – 18.4c, i

  16. PRECIPITATION REACTIONSSolubility of Precipitates OWL – 18.4a, d, f Lead(II) iodide

  17. Common Ion and Solubility PbCl2(s) Pb2+(aq) + 2 Cl-(aq) Ksp = 1.9 x 10-5 OWL – 18.5c OWL – 18.4i, k

  18. pH and solubility OWL – 18.5d OWL – 18.4m

  19. Did I cover these? • Use the common ion effect to predict relative solubility. • Use LeChatelier’s principle to predict the change in solubility of an ionic solid. • Given an ion, formulas containing the ion, and molarities of the ion determine the Ksp for each compound.

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