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L35S10_Weak+Acid-Base-Titration+04-19-10

L35S10_Weak+Acid-Base-Titration+04-19-10 - 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 (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 ©A.Pines,M.Kubinec,UCB L35-1 ChemQuiz© 34.3 For the Acids HA1 and HA2, pKa1 < pKa2. Which is true for tru HA1 + A2 A) K < 1 ©A.Pines,M.Kubinec,UCB HA1 HA2 - HA2 + B) K = 1 A1C) K > 1 L35-2 ChemQuiz© 34.4 For the Acids HA1 and HA2, pKa1 < pKa2. Which is true for tru HA1 + A2 - HA1 HA2 HA2 + A1- A) K = Ka1+Ka2 B) K = Ka1Ka2 C) K =Ka1/Ka2 ©A.Pines,M.Kubinec,UCB L34-4 ©A.Pines,M.Kubinec,UCB 1 Chem 1A L 35: "Weak Acid and Base, Titration" Weak Acid-Weak Base AcidpH ~ 1 ~4 ~7 ~ 10 ~ 13 HCl 1 HAc 2 H2 O 3 NH3 4 NaOH 5 L35-6 ©A.Pines,M.Kubinec,UCB 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) L35-7 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) L35-9 ©A.Pines,M.Kubinec,UCB 2 Chem 1A L 35: "Weak Acid and Base, Titration" pH Titration of a Weak Acid by a Strong Base D C B AE.P. Region A : 0.1 M HAc 2 3 + - A HA Summary TITRATIONH O + Ac HAc + H O WEAKWEAK-ACID BASE OH0.1 - x x x HA/AHA/ Buffer acid Expect: 1.0 < pH < 7.0 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 HAc +OHx Expect: x 7.0 < pH < 13.0 Assume 0.1-x ? 0.1 0.1x2 = Kb = 5.68 x 10-10 0.1- x pH = 8.88 0.1x2 = 0.1 Kb ©A.Pines,M.Kubinec,UCB x = 7.5x10-6 L29-8 pH Titration of a Weak Acid by a Strong Base D C OHB A HA/ HA/ABuffer AE.P. acid HA HA + OH- base H2O + A- acid base + OH©A.Pines,M.Kubinec,UCB L35-13 pH B Titration of a Weak Base by a Strong Acid B/BH+ Buffer BH+ E.P. base B + H3O+ acid base H2O + BH+ acid H3 O + + H3 O + ©A.Pines,M.Kubinec,UCB L35-14 ©A.Pines,M.Kubinec,UCB 3 Chem 1A L 35: "Weak Acid and Base, Titration" Region A : 0.1 M HAc HAc + H2O 0.1 - x H3O + Ac x x + - Expect: 1.0 < pH < 7.0 0.10.1 - x x2 Assume 0.1-x ≈ 0.1 0.1= Ka = 1.76 x 10-5 x = 1.33x10-3 L35-15 pH = 2.88 x2 = 0.1 Ka ©A.Pines,M.Kubinec,UCB 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 ©A.Pines,M.Kubinec,UCB B) = 4.0 C) > 4.0 L35-16 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 L35-20 0.10.1 - x pH = 8.88 x2 = 0.1 Kb ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB 4 Chem 1A L 35: "Weak Acid and Base, Titration" ChemQuiz© 35.4 35.4 Consider the titration of the following with a strong acid/base. For which is the pH at the wh pH equivalence equivalence point less than 7 ? A) HCl pKa ~ -7 B) HCOOH pKa ~ 3 C) NH3 pKb ~ 5 L35-21 ©A.Pines,M.Kubinec,UCB Lecture complete ©A.Pines,M.Kubinec,UCB L35-23 ©A.Pines,M.Kubinec,UCB 5 ...
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