L36S09_Buffers,+Acid+Strength+04-22-09

L36S09_Buffers,+Acid+Strength+04-22-09 - CHEM 1A, L 36:...

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Unformatted text preview: CHEM 1A, L 36: "Buffers, Acid Strength" Weak Acid/Base (HAc/Ac-) (HAc/Ac acid Weak Base/Acid (NH3/NH4+) NH3 + H2O base acid base HAc + H2O Summary + - base acid H3O+ + Ac - Ka = 1.8x10-5 1.8x10 pKa = 4.7 4.7 base base OH- + NH4+ Kb = 1.8x10-5 1.8x10 pKb = 4.7 4.7 base acid - acid + acid H2O + Ac- base acid HAc + OH - Kb = 5.6x10-10 5.6x10 pKb = 9.3 9.3 L36-4 - H2O + NH4+ base acid NH3 + H3O+ Ka = 5.6x10-10 5.6x10 pKa = 9.3 9.3 L36-5 + ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB Conjugate Acid/Base Pair HAc+H2O HAc+H Ka = + H3O ++Ac- + - H2O +Ac- HAc +OH- [H30 ][Ac ] [HAc] HAc] X [HAc][OH-] HAc][OH Kb = [Ac-] Ka Kb = [H30+][OH-] = Kw ©A.Pines,M.Kubinec,UCB L28-7 © 2004 M. Kubinec, A.Pines L36-1 ChemQuiz© 35.3 A solution of a) HCl b) HAc of pH = 3.0 is diluted x 10. 10. What is the new pH ? H2O HCl A) < 4.0 © 2004 M. Kubinec, A.Pines B) = 4.0 C) > 4.0 L36-2 ChemQuiz© 35.3a Solution pH = 3.0 [H3O+] = 10-3 H2O Thus initial [HCl] = 10-3 [HCl] Dilute x 10: [H3O+] = 10-4 pH = 4 A) < 4.0 © 2004 M. Kubinec, A.Pines HCl B) = 4.0 C) > 4.0 L36-3 © 2004 M. Kubinec, A. Pines 1 CHEM 1A, L 36: "Buffers, Acid Strength" ChemQuiz© 35.3b Solution pH = 3.0 [H3O+] = 10-3 Thus initial [HAc] >> 10-3 [HAc] Dilute x 10: initial [H3O+] = 10-4 H2O HAc + H2O A) < 4.0 © 2004 M. Kubinec, A.Pines H3O++ Ac+ produces more H3O B) = 4.0 C) > 4.0 + - HCl L36-4 Summary TITRATION WEAK-ACID BASE © 2004 M. Kubinec, A.Pines L36-5 Titration of a Weak Acid by a Strong Base D pH pH C B A HAc HAc/AcHAc/ Buffer OH- AcE.P. acid HAc + OH- base H2O + Ac- acid base + OH© 2004 M. Kubinec, A.Pines L36-6 © 2004 M. Kubinec, A. Pines 2 CHEM 1A, L 36: "Buffers, Acid Strength" Weak Acid/Base (HAc/Ac-) (HAc/Ac acid Weak Base/Acid (NH3/NH4+) NH3 + H2O base acid base HAc + H2O Summary + - base acid H3O+ + Ac - Ka = 1.8x10-5 1.8x10 pKa = 4.7 4.7 base base OH- + NH4+ Kb = 1.8x10-5 1.8x10 pKb = 4.7 4.7 base acid - acid + acid H2O + Ac- base acid HAc + OH - Kb = 5.6x10-10 5.6x10 pKb = 9.3 9.3 L36-4 - H2O + NH4+ base acid NH3 + H3O+ Ka = 5.6x10-10 5.6x10 pKa = 9.3 9.3 L36-5 + ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB Conjugate Acid/Base Pair HAc+H2O HAc+H Ka = + H3O ++Ac- + - H2O +Ac- HAc +OH- [H30 ][Ac ] [HAc] HAc] X [HAc][OH-] HAc][OH Kb = [Ac-] Ka Kb = [H30+][OH-] = Kw ©A.Pines,M.Kubinec,UCB L28-7 © 2004 M. Kubinec, A.Pines L36-7 Region C : 0.1 M AcAc - + H2O HAc +OHx Expect: 7.0 < pH < 13.0 x - 0.1 - x x2 Assume 0.1-x ≈ 0.1 0.1= Kb = 5.68 x 10-10 x = 7.5x10-6 L36-8 0.1- x 0.1- pH = 8.88 x2 = 0.1 Kb © 2004 M. Kubinec, A.Pines Region B: [HAc] ~ [Ac-] pH Buffer E.P. acid ½ E.P. © 2004 M. Kubinec, A.Pines HAc + OH- base H2O + Ac- acid base + OHL36-9 © 2004 M. Kubinec, A. Pines 3 CHEM 1A, L 36: "Buffers, Acid Strength" Region B: [HAc] ~ [Ac-] pH Buffer [HAc] = [Ac-] HAc] HAc + OH- H2O + AcAc- + H3O+ H2O + HAc K >> 1 + OH½ E.P. © 2004 M. Kubinec, A.Pines L36-10 pH Buffer Range [Ac-] pH = pKa + log [HAc] HAc] [Ac-] < [HAc] HAc] pKa+1 pKa pKa-1 1 [Ac-] > [HAc] HAc] 1 base form predominates acid form predominates ½ E.P. © 2004 M. Kubinec, A.Pines +OHL36-11 CO2(s) → CO2(g) + H2O → H2CO3 (aq)→ aq) H3O+ + HCO3- (aq) → H3O+ + CO3 2- (aq) HCO aq) CO aq) Flask 1, NaOH, pH 11 NaOH, - + H O+ → 2H O OH 3 2 Flask 2, phosphate buffer HPO42-/PO43pH 11 PO43- + H3O+ → HPO42- + H2O © 2004 M. Kubinec, A.Pines Buffer Demo L36-12 © 2004 M. Kubinec, A. Pines 4 CHEM 1A, L 36: "Buffers, Acid Strength" Buffer Range [Ac-] = 10 [HAc] HAc] [Ac-] = 0.1 [HAc] HAc] = [Ac ] pH = pKa + log 11 [A-] [HA] HA] = 10 Dilution: [Ac-] [Ac-] 10 [HAc] [HAc] [HAc] HAc] HAc] HAc] ∆pH = 0 L36-13 © 2004 M. Kubinec, A.Pines Henderson-Hasselbalch Acid H3PO4 pKa 2.1 7.1 12.4 6.1 10.2 4.75 L36-14 pH = pKa + log [A-] [HA] HA] H2PO4HPO42H2CO3 HCO3HAc © 2004 M. Kubinec, A.Pines ChemQuiz© 36.1 Which, when added to NH3 solution, forms a basic buffer (pH > 7)? 7)? pH > 7.0 [NH4+] [NH3] A) NaOH © 2004 M. Kubinec, A.Pines B) NaCl C) HCl L36-15 © 2004 M. Kubinec, A. Pines 5 CHEM 1A, L 36: "Buffers, Acid Strength" ChemQuiz© 36.2 Shown in yellow is the titration of HNO3 per mole KOH. Which is KOH. the correct curve for x10 dilution of HNO3? A) © 2004 M. Kubinec, A.Pines H2O HNO3 B) mol OHmol OH- C) mol OHL36-17 ChemQuiz© 36.3 Shown is in yellow the titration of HAc per mole KOH. Which is the KOH. correct curve for x10 dilution of HAc? HAc? A) © 2004 M. Kubinec, A.Pines H2O HAc B) mol OHmol OH- C) mol OHL36-19 Lecture Complete © 2004 M. Kubinec, A.Pines L36-21 © 2004 M. Kubinec, A. Pines 6 ...
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This note was uploaded on 04/24/2010 for the course CHEM 1A taught by Professor Nitsche during the Spring '08 term at University of California, Berkeley.

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