L36S07_Buffers, Acid Strength 04-18-07

L36S07_Buffers, Acid Strength 04-18-07 - 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 pKa = 4.7 base base OH- + NH4+ Kb = 1.8x10-5 pKb = 4.7 base acid - acid + acid H2O + Ac- base acid HAc + OH - Kb = 5.6x10-10 pKb = 9.3 L36-4 - H2O + NH4+ base acid NH3 + H3O+ Ka = 5.6x10-10 pKa = 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 1) < 4.0 2004 M. Kubinec, A.Pines 2) = 4.0 3) > 4.0 L36-2 pH Titration of a Weak Acid by a Strong Base D C B AE.P. A HA Summary TITRATION O + Ac HAc + H O H WEAK-ACID BASE OH0.1 - x 2 Region A : 0.1 M HAc 3 + - x x Expect: 1.0 < pH < 7.0 HA/AHA/ Buffer acid HA + OH- base H2O + A- acid base Assume 0.1-x ? 0.1 0.1x2 = Ka = 1.76 x 10-5 0.1- x pH = 2.88 0.1x2 = 0.1 Ka x = 1.33x10-3 L29-6 + OHA.Pines,M.Kubinec,UCB L29-4 A.Pines,M.Kubinec,UCB Region C : 0.1 M AcAc - + H2O 0.1 - x x2 Region B : [HA] ~ [HA] pH Buffer [A-] HAc +OH x Expect: x 7.0 < pH < 13.0 - Assume 0.1-x ? 0.1 0.1= Kb = 5.68 x 10-10 x = 7.5x10-6 L29-8 [HA] = [A-] 0.1- x 0.1- pH = 8.88 E.P. A.Pines,M.Kubinec,UBC x2 = 0.1 Kb A.Pines,M.Kubinec,UCB 2004 M. Kubinec, A.Pines HA + OH- H2O + AH2O + HA A- + H3O+ K >> 1 + L36-5 OHL30-4 2004 M. Kubinec, A. Pines 1 CHEM 1A, L 36: Buffers, Acid Strength" Titration of a Weak Acid by a Strong Base D pH pH C B A HA HA/AHA/ Buffer OH- AE.P. acid HA + OH- base H2O + A- acid base + OH 2004 M. Kubinec, A.Pines L36-6 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 L36-7 0.1- x 0.1- pH = 8.88 x2 = 0.1 Kb 2004 M. Kubinec, A.Pines Region B : [HA] ~ [A-] pH Buffer E.P. acid E.P. 2004 M. Kubinec, A.Pines HA + OH- base H2O + A- acid base + OHL36-8 2004 M. Kubinec, A. Pines 2 CHEM 1A, L 36: Buffers, Acid Strength" Region B : [HA] ~ [A-] pH Buffer [HA] = [A-] E.P. 2004 M. Kubinec, A.Pines HA + OH- H2O + AH2O + HA A- + H3O+ K >> 1 + OHL36-9 pH Buffer Range [A-] pH = pKa + log [HA] HA] [A-] [HA] HA] pKa+1 pKa pKa-1 <1 [A-] [HA] HA] >1 base form predominates acid form predominates E.P. 2004 M. Kubinec, A.Pines +OHL36-10 Buffer Range [A-] = 10 [HA] HA] [A-] = 0.1 [HA] HA] = [A ] pH = pKa + log 11 [A-] [HA] HA] [A-] [HA] HA] = 10 [A-] 10 Dilution: [HA] HA] [HA] HA] pH = 0 L36-11 2004 M. Kubinec, A.Pines 2004 M. Kubinec, A. Pines 3 CHEM 1A, L 36: Buffers, Acid Strength" Henderson-Hasselbach Acid H3PO4 pKa 2.1 7.1 12.4 6.1 10.2 4.75 L36-12 [A-] pH = pKa + log [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] 1) NaOH 2004 M. Kubinec, A.Pines 2) NaCl 3) HCl L36-13 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? 1) 2004 M. Kubinec, A.Pines H2O HNO3 2) mol OHmol OH- 3) mol OHL36-15 2004 M. Kubinec, A. Pines 4 CHEM 1A, L 36: Buffers, Acid Strength" 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? 1) 2004 M. Kubinec, A.Pines H2O HAc 2) mol OHmol OH- 3) mol OHL36-17 Lecture Complete 2004 M. Kubinec, A.Pines L36-19 2004 M. Kubinec, A. Pines 5 ...
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