1 / 17

Lecture 9

Lecture 9. Acid-Base Equilibria -I. We titrate with strong acids ONLY!. Strong acids:. HCl HBr HI HNO 3 H 2 SO 4 HClO 4. (HO) n E=O. (HO) n EO 2. Weak acid. Strong acid. _. Concentrations below 10 -8 M do not affect the pH value.

haruko
Download Presentation

Lecture 9

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 9 Acid-Base Equilibria -I

  2. We titrate with strong acids ONLY! Strong acids: HCl HBr HI HNO3 H2SO4 HClO4 (HO)nE=O (HO)nEO2 Weak acid Strong acid

  3. _

  4. Concentrations below 10-8M do not affect the pH value 10-6 -10-8 require special treatment (in practice, this will be still affected mostly by CO2 and NH3 from air) Only concentrations above 10-6M may change the pH value – and only in absence of other acids or bases Conclusion:we cannot titrate low concentrations of acids or bases in water

  5. Weak acids and bases: Ka is a small number (<< 1)

  6. acid base HA  A + H+ acid base KaKb = A + H2O HA + OH- + HA  A + H+ A + H2O  HA + OH- = [H+][OH-] H2O  H+ + OH-

  7. pH value of weak acid solution (C> 10-3 M) The main source of H+ is HA, not H2O HA  A + H+ [A] = [H+] [HA] = C - [H+] A small number [H+]2 = KaC Check the resulting [H+] and correct if necessary

  8. Any acid is “strong” at very low concentration – but it does not change the pH!

  9. pH value of weak base solution (C> 10-3 M) The main source of OH- is A, not H2O A + H2O HA + OH- [HA] = [OH-] [A] = C - [OH-] A small number KaKb =[H+][OH-]=10-14 [OH-]2 = KbC Check the resulting [OH-] and correct if necessary

  10. pH value of mixture of a weak base and weak acid (C> 10-3 M) HA  A + H+ At high concentrations, [A]=CA and [HA]=CHA

  11. pH value of mixture of a weak base and weak acid (C> 10-3 M) buffer • pH does not change when you vary • concentration a little In practice, one buffer pair (acid+ conjugate base) determines the pH value of the whole multicomponent mixture

  12. A complex mixture: Harris, p. AP12 pKa=9.24 0.1 M 0.1 M pH= 9.24 All other species in the system (indicator, any admixtures, …) will follow the pH determined by the buffer

  13. Enzyme activity as a function of pH

  14. or Effect of [A]/[HA] on pH Effect of pH on [A]/[HA]

  15. pK=5

  16. pH calculations: pH = -log[H+] KaKb =[H+][OH-]=10-14 K>1 Strong acid or strong base [H+]=Cacid [OH-]=Cbase K<<1 Weak acid or weak base A mixture of a weak base and weak acid

More Related