38 - Determining Krxn using Ka Determining Krxn using Ka...

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CH 3 COO 1- + H CN CH 3 COO H + CN 1- Section 12.4 Determining K rxn using K a K = [CH 3 COO 1- ][ H CN ] [CH 3 COO H ][ CN 1- ] If K is >1, we should leave the room. If K is <1, we’re going to be OK. When we finish with K a , you’ll know. CH 3 COO 1- + H CN CH 3 COO H + CN 1- K = [products] [reactants] = [ CH 3 COO 1- ][ H CN ] [ CH 3 COO H ][ CN 1- ] [ CH 3 COO 1- ][ H 3 O 1+ ][ H CN ] [ CH 3 COO H ][ H 3 O 1+ ][ CN 1- ] = K a (CH 3 COOH) = K a (HCN) [ H 3 O 1+ ] [ H 3 O 1+ ] * Section 12.6 & 7 = K a (reacting acid) K a (produced acid) K rxn Determining K rxn using K a CH 3 COO 1- (aq) + H 3 O 1+ (aq) CH 3 COO H (aq) + H 2 O (l) K a ( CH 3 COO H ) = [ CH 3 COO 1- ][ H 3 O 1+ ] [ CH 3 COO H ] H CN (aq) + H 2 O (l) CN 1- (aq) + H 3 O 1+ (aq) K a ( H CN ) = [ CN 1- ][ H 3 O 1+ ] [ H CN ] Section 12.6 & 7 Determining K rxn using K a K a Table 12.3: acid-base table H 3 O 1+ 1.0 H 2 O acid base HNO 3 >>1.0 NO 3 1- H 2 SO 4 >>1.0 HSO 4 1- HX (Cl, Br, I) >>1.0 X 1- HClO 4 >>1.0 ClO 4 1- H 2 O 10 -14 OH 1- NH 3 <<10 -14 NH 2 1- OH 1- <<10 -14 O 2- HF ~ 10 -3 F 1- HC 2 H 3 O 2 1.8 x 10 -5 C 2 H 3 O 2 1- SA WA SB WB HCN 4.0 x 10 -10 CN 1- If I added acetic acid to sodium cyanide, should I leave the room? K = K a (CH 3 COOH) K a (HCN) = 1.8 x 10 -5 4.0 x 10 -10 = 4.5 x 10 4 Yes Section 12.6 & 7 K > 10 3 , use single arrow K < 10 3 , use double arrows X CH 3 COO H + CN 1- CH 3 COO 1- + H CN Determining K rxn using K a A simple matter of filling in conjugate base conjugate acid HCO 3 1- + HPO 4 2- acid base Section 12.4 What? How do I figure out which one is the acid? When we finish with K a , you’ll know. + conjugate base (subtract an H 1+ ) conjugate Acid (add an H 1+ ) CO 3 2- H 2 PO 4 1- Bronsted Acid-Base Reactions
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HCO 3 1- + HPO 4 2- acid base Section 12.6 & 7 © Lori Petrovich conjugate base (subtract an H 1+ ) conjugate acid (add an H 1+ ) CO 3 2- +H 2 PO 4 1- HCO 3 1- + HPO 4 2- acid base conjugate base (subtract an H 1+ ) conjugate acid (add an H 1+ ) H 2 CO 3 + PO 4 3- = 7.6 x 10 -4 4.7 x 10 -11 K = K a (HCO 3 1- ) K a (H 2 PO 4 1- ) = 6.2 x 10 -8 = 1.1 x 10 -6 4.8 x 10 -13 K = K a
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This note was uploaded on 06/08/2008 for the course CH 101 taught by Professor Bigham during the Fall '08 term at N.C. State.

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38 - Determining Krxn using Ka Determining Krxn using Ka...

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