TTh_9 - Organic Lecture Series CH 310/318 M LECTURE 9...

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Organic Lecture Series 1 CH 310/318 M LECTURE 9 Textbook Assignment: Chapter 4-Begin Today’s Topics: Acidity; Acidity; pKa pKa ; Mechanisms ; Mechanisms Notice & Announcements: HW 4 Posted Organic Lecture Series 2 Acids and Acids and Bases Bases Chapter 4 Chapter 4
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Organic Lecture Series 3 Weak Acids and Bases An equilibrium expression for the dissociation of any uncharged acid, HA, is written as: HA + H 2 O [H 3 O + ][A - ] [HA][H 2 O] K eq A - + H 3 O + = Organic Lecture Series 4 Weak Acids and Bases Weak Acids and Bases ¾ Water is a solvent and its concentration is a constant equal to approximately 55.5 mol/L. ¾ We can combine these constants to give a new constant, K a , called an acid dissociation acid dissociation constant constant. K 2 K a 3 O + - ] [HA] ==
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Organic Lecture Series pK pK a HI I - HBr Br - HCl Cl - H 2 SO 4 HSO 4 - H 2 O H 3 O + H 3 PO 4 H 2 4 - C 6 H 5 COOH C 6 H 5 COO - CH 3 COOH CH 3 COO - H 2 CO 3 HCO 3 - H 2 S HS - NH 3 4 + C 6 H 5 OH C 6 H 5 O - HCO 3 - CO 3 2- CH 3 2 CH 3 3 + H 2 O HO - CH 3 CH 2 OH CH 3 CH 2 O - HC CH HC C - H 2 H - 3 2 - CH 2 =CH 2 CH 2 - CH 3 CH 3 CH 3 CH 2 - Acid Formula p K a Conju gate Base Ethan e Ammonia Ethan ol Water Bicarbonate ion Phenol Ammonium ion Carbonic acid Acetic acid 35 25 Benzoic acid Phosphoric acid Sulfuric acid Hydrogen chloride Hydrogen bromide Hydrogen iodide 51 38 10.33 15.7 15.9 4.76 6.36 9.24 9.95 -5.2 -7 -9 -8 4.19 2.1 -1.74 Hydronium ion Stronger conju gate base Weaker conjugate acid Methylammonium ion 10.64 Hydrogen sulfide 7.04 Acetylene Hydrogen Ethy lene 44 Organic Lecture Series 6 Acid -Base Base Equilibria Equilibria • Equilibrium favors reaction of the stronger acid and stronger base to give the weaker acid and weaker base. CH 3 COOH 3 CH 3 - 4 + ++ Ammonia (stronger base ) Acetate ion (weaker base) Acetic acid p K a 4.76 (stronger acid) Ammonium ion p K a 9.24 (weaker acid) Favors the side with the highest pKa (i.e weaker acid)
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Organic Lecture Series 7 • Consider the reaction between acetic acid and sodium bicarbonate. ± write the equilibrium as a net ionic equation.
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This note was uploaded on 03/18/2012 for the course CH 310 M taught by Professor Iverson during the Spring '09 term at University of Texas at Austin.

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TTh_9 - Organic Lecture Series CH 310/318 M LECTURE 9...

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