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Topics. H + Acids and Bases Definition of pH Reversible reactions, equilibrium, mas action HendersonpHasselbalch equation Buffers. Buffer capacity. H +. Suppose chloride acid dissolved in water. HCl H + + Cl -.

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  1. Topics • H+ • Acids and Bases • Definition of pH • Reversible reactions, equilibrium, mas action • HendersonpHasselbalch equation • Buffers. Buffer capacity

  2. H+ Suppose chloride acid dissolved in water HCl H+ + Cl- The entity H+, hydrogen stripped from the electron, is simply a proton, without electronic cloud, with dimensions at least 4 orders smaller than a real atom. Its strong electrical field Impedes a free existence. What really happens, upon dissolution of HCl in water is: HCl + H2O H3O+ + Cl- H3O+ H2O + H+ HCl H++ Cl- [H+]

  3. Rutherford-Thompson atom: Dimensions 10-15(Fermi) 10-10 (Å) m

  4. Acids and Bases Brønsted-Lewy Concept (1923) Acid HA H+ + A- Base B- + H+ BH Arrhenius Concept (1890) Acid HA H+ + A- Base COH C+ + OH- Acid + base salt + water 2NaOH + H2SO4 Na2SO4 + 2H2O Water has amphoteric character 2H2O H3O- + H+

  5. pH, reversible reaction, equilibrium, mass action pH Reversible Reactions – Rate constants - Equilibrium BA B + A K1 k-1

  6. Henderson-Hasselbalch equation K1 k-1 HCl H+ + Cl- At equilibrium

  7. Buffers and Buffer capacity In a given pH, β is a function of pH and buffer concentration

  8. Bibliography • Bockris, J.O’M and Reddy, A.K.N.: Modern Electrochemistry. Plenum Press, 1970. Vol.1, 1970. Chap. 5. Protons in solution.

  9. Questions • For a [H+] of 10-10M to 10-1M, in steps fo 10-3M, draw a plot of pH x [H+]. • Consider 1 L of a solution of a buffer of pK=7.5 amd concentration of 10 mM. Starting with a buffer base concentration of 9,9 mM, add progressively a strong acid, in amounts of 0.05 mmol. At equilibrium draw the curve relating pH to the total amount of acid added. Where is the point of maximal buffering power? • Suppose a buffer if pK=7.0 in concentration of 5 mM. What are the concentrations of acid and base for buffering a solution at a pH of 6,0.

  10. Medidas de pH Eletródios Indicadoresfluorescentes Bibliografia Koryta, J.: Ion-Selective Electrodes. 1974. Cambridge University Press. Vanysek, P.> The glass pH electrode.The Electrochemical Society Interface. 2004 Lakowicz, J.R.: Principles of fluorescence spectroscopy. 2nd ed., 1999. Fluwer Academy/Plenum Press

  11. Electrochemical potential of a solute in a phase – Macroscopic view Thermal energy T (K) C2 ø2 C1 1 C: concentration, mol/l Ø: Electrical potential, V M R= 8.3 J mol-1 K-1

  12. Thermal energy – microscopic view Thermal energy Bezanilla simulation

  13. + + - - Campos elétricos – forças elétricas Força elétrica – lei de Coulomb Diferença de potencial elétrico Campo elétrico

  14. Membrane (M) Properties C2 ø2 C1 1 M 1. Impermeable membrane 2. Membrane permeable to solutes =0 3. Membrane permeable to cations or to anions =0

  15. Ion Exchangers – Glass Electrodes - - - - - - - - - - H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

  16. BCECF

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