04-10_AB_equilibria_3_web - ACIDBASEEQUILIBRIA a HA K 0.01c...

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ACID-BASE EQUILIBRIA K a ≤ 0.01c HA K a = 1.75 x 10 -5
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The reaction substrates and products are in equilibrium , and are linked by the equilibrium equation: - + + + A O 3 H a K O 2 H HA ] HA [ ] A ][ O 3 H [ a K - + = where K a is the acid dissociation constant. Weak acids and bases (quantitative aspects): The reaction stays at equilibrium!
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a K A O H O H HA ; 3 2 - + + + ] [ ] ][ 3 [ HA A O H K - + = α As before, “[ ]s” denote the equilibrium concentrations
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x, [H 3 O + ] = [A - ] x HA c x x a K - = For calculation applications: if K a ≤ 0.01c HA a simplification is applicable: HA c 2 x a K = and since pH = -log[H 3 O + ], pH = -log[x]
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+ + - + O H COO CH a K O H COOH CH 3 3 2 3
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COMPLEXOMETRY (with EDTA; Harris, pp. 236- 257)
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  EDTA: a very useful chelating agent  EDTA = ethylenediaminetetraacetic acid: H 2 C N COOH COOH COOH COOH N H 2 C
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COMPLEXOMETRY (with EDTA; Harris, pp. 236- 257)        1. Complex Formation Processes Many  metal  cations  form  slightly  dissociated  complexes  with ligands , usually small molecules or anions.               The  complex  formation  process  and  the  complex  compound properties have numerous applications in Analytical Chemistry, in particular, in determination of a large number of metals in aqueous media. In  the  complex  formation  process  a  binding  site  on  the  ligand,  to coordinate a central metal cation, is a pair of unshared electrons on N,  O,  S.    (e.  g.,  N:).    The  coordination  number   determines  the number of complexing groups (or ligands) per the central cation.
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Ag +  + NH 3     Ag(NH 3 ) + the  1 st  formation (or  stability) constant  for  this  reaction is: K f Ag NH Ag NH , [ ( ) ] [ ][ ] 1 3 3 = + + Ag(NH 3 ) + + NH 3 Ag(NH 3 ) 2 + the 2 nd  formation constant for this reaction is: K f Ag NH Ag NH NH , [ ( ) ] [ ( ) ][ ] 2 3 2 3 3 = + +
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Overall reaction: Ag +  + 2NH 3    Ag(NH 3 ) 2 + K f Ag NH Ag NH = + + [ ( ) ] [ ][ ] 3 2 3 2 the overall stability constant: K f  = K f,1    K f,2  = 2.5 × 10 7
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  A  chelating  agent : an  organic  compound,  usually  a weak acid or base that has two or more groups capable of complexing  with a metal ion. H
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This note was uploaded on 03/06/2011 for the course CHEMISTRY 222 taught by Professor Mcdonald during the Spring '11 term at University of Illinois, Urbana Champaign.

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04-10_AB_equilibria_3_web - ACIDBASEEQUILIBRIA a HA K 0.01c...

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