CH302_030111 - Polyprotic Acids More than one acid/base...

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Principles of Chemistry II © Vanden Bout Polyprotic Acids More than one acid/base group
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Principles of Chemistry II © Vanden Bout Monoprotic Acid Nitric Acid
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Principles of Chemistry II © Vanden Bout Polyprotic Acid Phosphoric Acid
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Principles of Chemistry II © Vanden Bout Polyprotic Acid Phosphoric Acid
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Principles of Chemistry II © Vanden Bout Polyprotic Acids Acids that have more than one proton to lose Now we need to keep track of all the "forms" of the acid Monoprotic HA , A - Diprotic H 2 A, HA - , A 2- Triprotic H 3 A, H 2 A - , HA 2- , A 3-
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Principles of Chemistry II © Vanden Bout Polyprotic Acid Phosphoric Acid + H + - - - + H + + H + - - -
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Principles of Chemistry II © Vanden Bout For example Sulfuric Acid H 2 SO 4 (aq) H + (aq) + HSO 4 - (aq) HSO 4 - (aq) H + (aq) + SO 4 2- (aq) K a1 = [H + ][HSO 4 - ] [H 2 SO 4 ] Equilibrium for the ±rst proton coming "off" = 10 3 K a2 = [H + ][SO 4 2- ] [HSO 4 - ] =1.2 x10 -2 Equilibrium for the next proton coming "off"
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Principles of Chemistry II © Vanden Bout Key Question What is in solution! H 2 A (aq) H + (aq) + HA - (aq) HA - (aq) H + (aq) + A 2- (aq) K a1 = [H + ][HA - ] [H 2 A] K a2 = [H + ][A 2- ] [HA - ] we'll reduce all such problems to 1 or 2 major forms of the acid. First ±gure out which ones will be in solution
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Principles of Chemistry II © Vanden Bout Carboxylic Acid R carbon double bonded to an oxygen bonded to carbon on one side OH on the other side C O OH Common Acetic Acid (vinegar)
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Principles of Chemistry II © Vanden Bout Citric Acid
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Principles of Chemistry II © Vanden Bout Citric Acid K a1 = 7.4 x 10 -4 K a2 = 1.7 x 10 -5 K a3 = 4.0 x 10 -7 What is the pH of 1M Citric Acid? Imagine that it was monoprotic K a1 = [H + ][H 2 A - ] [H 3 A ] (x)(x) Ca - x (x)(x) Ca = = Weak Acid [H + ] = x = K a C a = (7.4 x 10 -4 )(1) = 0.027
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Principles of Chemistry II © Vanden Bout K a2 = 1.7 x 10 -5 Assuming that [H + ] =.027 what is the ratio of deprotonated to protonated for the second proton?
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This note was uploaded on 03/27/2011 for the course CHEM 302 taught by Professor Mccord during the Spring '10 term at University of Texas at Austin.

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CH302_030111 - Polyprotic Acids More than one acid/base...

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