L35S09_Weak+Acid-Base-Titration+04-20-09

L35S09_Weak+Acid-Base-Titration+04-20-09 - Chem 1A L...

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Unformatted text preview: Chem 1A L 35: "Weak Acid and Base, Titration" 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 ©A.Pines,M.Kubinec,UCB L35-1 ChemQuiz© 34.4 For the Acids HA1 and HA2, pKa1 < pKa2. Which is true for HA1 + A) K < 1 ©A.Pines,M.Kubinec,UCB HA1 HA2 A2- HA2 + B) K = 1 A1C) K > 1 L35-2 Weak Acid-Weak Base pH ~ 1 ~4 ~7 ~ 10 ~ 13 HCl 1 HAc 2 H2O 3 NH3 4 NaOH 5 L35-4 ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB 1 Chem 1A L 35: "Weak Acid and Base, Titration" ChemQuiz© 35.1 If solutions 1 and 5 are mixed, what will be the: mixed, pH: A) Acidic A) ©A.Pines,M.Kubinec,UCB B) Neutral B) C) Basic C) L35-5 ChemQuiz© 35.2 If solutions 2 and 4 are mixed, what will be the: mixed, pH: A) Acidic A) ©A.Pines,M.Kubinec,UCB B) Neutral B) C) Basic C) L35-7 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 + OH©A.Pines,M.Kubinec,UCB L29-4 ©A.Pines,M.Kubinec,UCB Region C : 0.1 M AcAc - + H2O 0.1 - x x2 HAc +OHx 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 0.1- x 0.1- pH = 8.88 x2 = 0.1 Kb ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB 2 Chem 1A L 35: "Weak Acid and Base, Titration" 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©A.Pines,M.Kubinec,UCB L35-11 Titration of a Weak Base by a Strong Acid pH pH B B/BH+ Buffer BH+ E.P. base B + H3O+ acid base H2O + BH+ acid H3O+ + H3O+ ©A.Pines,M.Kubinec,UCB L35-12 Region A : 0.1 M HAc HAc + H2O 0.1 - x x2 H3O++ Ac- 1.0 < pH < 7.0 x x Assume 0.1-x ≈ 0.1 0.1- + - Expect: 0.1- x 0.1- = Ka = 1.76 x 10-5 x = 1.33x10-3 pH = 2.88 x2 = 0.1 Ka ©A.Pines,M.Kubinec,UCB L35-13 ©A.Pines,M.Kubinec,UCB 3 Chem 1A L 35: "Weak Acid and Base, Titration" 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 ©A.Pines,M.Kubinec,UCB B) = 4.0 C) > 4.0 L35-14 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 L35-17 0.1- x 0.1- pH = 8.88 x2 = 0.1 Kb ©A.Pines,M.Kubinec,UCB ChemQuiz© 35.4 Consider the titration of the following with a strong acid/base. For which is the pH at the equivalence point less than 7 ? A) HCl pKa ~ -7 B) HCOOH pKa ~ 3 C) NH3 pKb ~ 5 L35-18 ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB 4 Chem 1A L 35: "Weak Acid and Base, Titration" Lecture complete ©A.Pines,M.Kubinec,UCB L35-20 ©A.Pines,M.Kubinec,UCB 5 ...
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