L36S10_Buffers,+Acid+Strength+04-21-10

L36S10_Buffers,+Acid+Strength+04-21-10 - 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 (NH 3/NH 4+) 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 ? H2 O HCl A) < 4.0 © 2004 M. Kubinec, A.Pines B) = 4.0 C) > 4.0 L36-2 Summary TITRATION WEAKWEAK-ACID BASE © 2004 M. Kubinec, A.Pines L36-5 © 2004 M. Kubinec, A. Pines 1 CHEM 1A, L 36: "Buffers, Acid Strength" pH Titration of a Weak Acid by a Strong Base D C OHB A HAc/ HAc/AcBuffer AcE.P. acid HAc HAc + OH- base H2O + Ac- acid base + OH© 2004 M. Kubinec, A.Pines L36-6 Weak Acid/Base (HAc/Ac -) (HAc/Ac acid Weak Base/Acid (NH 3/NH 4+) 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 Kb = [HAc][OH-] HAc][OH [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 0.1 - x x2 HAc +OH x Expect: 7.0 < pH < 13.0 x - Assume 0.1-x ≈ 0.1 0.1= Kb = 5.68 x 10-10 x = 7.5x10-6 L36-8 0.10.1 - x pH = 8.88 x2 = 0.1 Kb © 2004 M. Kubinec, A.Pines © 2004 M. Kubinec, A. Pines 2 CHEM 1A, L 36: "Buffers, Acid Strength" Region pH Buffer B: [HAc] ~ [Ac-] [HAc] E.P. acid ½ E.P. © 2004 M. Kubinec, A.Pines HAc + OH- base H2O + Ac- acid base + OHL36-9 Region pH Buffer B: [HAc] ~ [Ac-] [HAc] [HAc] = [Ac-] HAc + OH- H2O + AcAc- + H3O+ H2O + HAc K >> 1 + OH½ E.P. © 2004 M. Kubinec, A.Pines L36-10 pH Buffer Range pH = pKa + log [Ac-] [Ac-] [HAc] HAc] [Ac-] [HAc] pKa+1 pKa pKa-1 [HAc] <1 >1 base form predominates acid form predominates ½ E.P. © 2004 M. Kubinec, A.Pines +OHL36-11 © 2004 M. Kubinec, A. Pines 3 CHEM 1A, L 36: "Buffers, Acid Strength" CO2(s) CO2(g) + H2O H2CO3 (aq) HCO CO H3O+ + HCO3- (aq) H3O+ + CO3 2- (aq) Flask 1, NaOH, pH 11 OH- + H3O+ 2H2O Flask 2, phosphate buffer HPO42-/PO43pH 11 PO43- + H3O+ HPO42- + H2O © 2004 M. Kubinec, A.Pines Buffer Demo L36-12 Buffer Range [Ac-] = 10 [HAc] HAc] [Ac-] = 0.1 [HAc] HAc] = [Ac ] pH = pKa + lo1 pK 1g [A-] [HA] HA] = 10 Dilution: [Ac-] [Ac-] 10 [HAc] [HAc] [HAc] HAc] HAc] HAc] ΔpH = 0 L36-13 © 2004 M. Kubinec, A.Pines HendersonHenderson-Hasselbalch Acid H3PO4 pKa 2.1 7.1 12.4 6.1 10.2 4.75 L36-14 [A-] pH = pKa + log pK log [HA] HA] H2PO4HPO42H2CO3 HCO3HAc © 2004 M. Kubinec, A.Pines © 2004 M. Kubinec, A. Pines 4 CHEM 1A, L 36: "Buffers, Acid Strength" ChemQuiz© 36.1 Which, when added to NH3 solution, forms a basic basic buffer (pH > 7)? pH > 7.0 [NH4+] [NH3] A) NaOH © 2004 M. Kubinec, A.Pines B) NaCl C) HCl L36-15 ChemQuiz© 36.2 Shown in yellow is the titration of HNO3 per mole KOH. Which is KOH. the the correct curve for x10 x10 dilution of HNO3? A) © 2004 M. Kubinec, A.Pines H2 O 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 correct curve for x10 dilution dilution of HAc? HAc? A) © 2004 M. Kubinec, A.Pines H2 O HAc B) mol OHmol OH- C) mol OHL36-19 © 2004 M. Kubinec, A. Pines 5 CHEM 1A, L 36: "Buffers, Acid Strength" Lecture Complete © 2004 M. Kubinec, A.Pines L36-21 © 2004 M. Kubinec, A. Pines 6 ...
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