Analytical Chem istry - DePauw University

Chapter 9 Titrimetric Methods523displacement of Pb 2+ by Zn 2+ lead to the reporting of too much ortoo little sulfate?(c) In a typical analysis, a 25.00-mL sample of an industrial effluentwas carried through the procedure using 50.00 mL of 0.05000 MEDTA. Titrating the excess EDTA required 12.42 mL of 0.1000M Mg 2+ . Report the molar concentration of SO 4 2– in the sampleof effluent.42. Table 9.10 provides values for the fraction of EDTA present as Y 4- , a Y 4–.Values of a Y 4– are calculated using the equationα Y4− =4−[ Y ]CEDTAwhere [Y 4- ] is the concentration of the fully deprotonated EDTA andC EDTA is the total concentration of EDTA in all of its forms2+ +C EDTA 6 5 4= [ HY ] + [ HY ] + [ HY]+2−[ HY ] + [ HY ] + [ HY−3 2−] + [ Y ]3−4Using the following equilibria2+ + +HY ( aq) + HO() l HO ( aq) + HY ( aq )6 2 3 5+ +HY ( aq) + HO() l HO ( aq) + HY( aq )5 2 3 4+ −HY( aq) + HO() l HO ( aq) + HY ( aq )4 2 3 3− + 2−HY ( aq) + HO() l HO ( aq) + HY ( aq )3 2 3 22− + 3−HY ( aq) + HO() l HO ( aq) + HY ( aq )2 2 33− + 4−HY ( aq) + HO() l HO ( aq) + Y ( aq )2 3K a1K a2K a3K a4K a5K a6Some of the problems that follow require one ormore equilibrium constants or standard state potentials.For your convenience, here are hyperlinksto the appendices containing these constantsAppendix 10: Solubility ProductsAppendix 11: Acid Dissociation ConstantsAppendix 12: Metal-Ligand Formation ConstantsAppendix 13: Standard State Reduction Potentialsshow thatα Y4−=K K K K K Ka1 a2 a3 a4 a5 a6dwhered = + 6+ + 5K + + 4[ H ] [ H ] [ H ] K K ++ 3[ H ] K K Ka1 a2 a3a1 a1 a2+ 2+ [ H ] K K K K +a1 a2 a3 a4+ 1[ H ] K K K K K + Ka1 a2 a3 a4 a5 a 1K a2K a3K a4K a5K a6