1 / 19

Outline: 2/28/07

Outline: 2/28/07. Seminar – Friday @ 4pm Pick up Quiz #5 – from me Mid-term grades due today…. Today: Chapter 17 (cont’d). Acid-base Equilibria : More weak acid/base/salt pH calcs The relationship K a  K b = K w Hydrolysis & Neutralization. + 1.0 +0.5 - 1.0 .

kristen-wong
Download Presentation

Outline: 2/28/07

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. Outline: 2/28/07 • Seminar – Friday @ 4pm • Pick up Quiz #5 – from me • Mid-term grades due today… • Today: Chapter 17 (cont’d) • Acid-base Equilibria: • More weak acid/base/salt pH calcs • The relationship Ka Kb = Kw • Hydrolysis & Neutralization

  2. +1.0 +0.5-1.0 -2x -x +2x (change) neglect (2x)2 Keq = (2)2(1.5) Quiz #5 3. 2 NO(g) + O2(g) 2NO2(g) K is small 1.0 1.0 1.0 (init) 2.0 1.5 0.0 (init) 2 - 2x 1.5-x 2x (equil.)

  3. Acids & Bases: Chapter 17 • Any chemical that donates a proton is a Bronsted-Lowry acid… any chemical that accepts a proton is a Bronsted-Lowry base. • HCl  H+ + Cl- • HCl + H2O  H3O+ + Cl- acid base Conjugate acid Conjugate base

  4. Acids & Bases: • Some chemicals can do both: they are called “amphoteric” • HSO3- + H2O  H3O+ + SO32- acid base Conjugate acid Conjugate base • HSO3- + H2O  H2SO3 + OH- base acid Conjugate acid Conjugate base

  5. Calculation Examples: • Calculate the pH of a solution of 2.510-2 M HClO4? (perchloric acid) • Step #1:identify the acid • If strong acid  complete dissociation • HClO4H++ ClO4- • 2.510-2 M 0 0 init • 0 equil 2.510-2M 2.510-2 M • Step #2: pH = - log [H+]- log (2.510-2) = 1.60

  6. Examples: • Calculate the pH of a solution of 2.510-2 M HClO? (hypochlorous acid) • Step #1:identify the acid • if weak acid  look up Ka = 3.5  10-8 • HClOH++ ClO- • 2.510-2 M 0 0 init • (2.510-2-x)M x M x M equil • Step #2: pH = - log [H+]- log (2.710-5) = 4.56

  7. Weak Base Example: • Calculate the pH of a solution of 2.510-2 M trimethylamine (CH3)3N ? • Step #1:identify it as a weak base • look up Kb = 6.5  10-5 • (CH3)3N + H2OOH-+ (CH3)3NH+ • 2.510-2 M 0 0 init • (2.510-2-x)M x M x M equil • Step #2: pOH = - log [OH-]- log (1.310-3) = 2.89 • Step #3: 14 -pOH = pH = 11.11

  8. Problem solving overview: • Skills needed to solve these problems: • 1) Identify strong/weak acid/bases • 2) Identify conjugate acid/bases & salts • 3) Solving equilibrium problems • 4) Identifying & making the correct Keq Know the 6 strong acids / 4 strong bases… Know solubility rules & acid/base definitions Solve for x…forward or backwards... Add equations to make new one & K’s multiply

  9. Keq Ka1 Ka2 Acids & Bases: What are Ka & Kb? Ka • HA  H+ + A- • H2A  H+ + HA- • HA- H+ + HA- • B+ + H2O  H+ + BOH • BOH  B+ + OH- • A-+ H2O HA + OH- • H2O  H+ + OH-

  10. Keq Ka1 Ka2 • “polyprotic acids” Acids & Bases: What are Ka & Kb? • H2A  H+ + HA- • HA- H+ + HA-

  11. Keq Ka1 Ka2 Acids & Bases: What are Ka & Kb? Ka • HA  H+ + A- • H2A  H+ + HA- • HA- H+ + HA- • B+ + H2O  H+ + BOH Ka • BOH  B+ + OH- • A-+ H2O HA + OH- • H2O  H+ + OH-

  12. Keq Acids & Bases: What are Ka & Kb? • B+ + H2O  H+ + BOH Ka • “Hydrolysis” • (often metal salts….)

  13. Keq Ka1 Ka2 Acids & Bases: What are Ka & Kb? Ka • HA  H+ + A- • H2A  H+ + HA- • HA- H+ + HA- • B+ + H2O  H+ + BOH Ka Kb • BOH  B+ + OH- • A-+ H2O HA + OH- Kb • H2O  H+ + OH-

  14. Keq Acids & Bases: What are Ka & Kb? • A-+ H2O HA + OH- Kb • “hydrolysis” (conjugate base salts)

  15. Keq Ka1 Ka2 Acids & Bases: What are Ka & Kb? Ka • HA  H+ + A- • H2A  H+ + HA- • HA- H+ + HA- • B+ + H2O  H+ + BOH Ka Kb • BOH  B+ + OH- • A-+ H2O HA + OH- Kb Kw • H2O  H+ + OH-

  16. Keq • H2O  H+ + OH- Kw • Or: • KaKb =Kw Acids & Bases: What are Ka & Kb? Ka • HA  H+ + A- • A-+ H2O HA + OH- Kb Remember: Hess’ Law

  17. Example: • Determine Keq for: • HCO3- + OH-  CO32-+ H2O • Step #1:identify the acid • H2CO3 (carbonic acid) • HCO3- H++ CO32- Ka2 • 4.810-11 • Step #2: what needs to be added? • H++ OH-  H2O • 1/Kw 1/1.010-14 Keq = 4.810-11 / 1.010-14

  18. Let’s try some more examples • The pH of an 0.0222 M solution of a weak acid is 5.43 Which acid is it? • HAH++ A- • (0.0222 -x) M x M x M Equil • You knowx = 10-5.43 = 3.71  10-6 • Solve forKeq • K = x2/ (0.0222 - x) = (3.71e-6)2/(0.0222) • = 6.210-10 App. E:HCN

  19. Worksheet 7 Try some more…

More Related