University:
California State University, Northridge
Course:
CHEM 321/L | Chemical Analysis I and Lab
Academic year:

2011
Views:

259

Pages:

2
Author:

sunnnnyaaets

Solutions for Complexometric Titrations Exercises 1. The fraction of EDTA that is in the fully ionized form (Y4-) is given by αY4-. As the solution becomes more basic and the pH increases, more of the acidic hydrogens are removed from EDTA and αY4 increases. 2. KNf = αY4-Kf = (0.041)(6.17 x 108) = 2.5 x 107 at pH = 9, αY4- = 0.041 and for Mg2+, Kf = 108.79 = 6.17 x 108 3. A metal ion indicator is a substance that complexes metal ions and has a different color in solution in the free form than when complexed. As the EDTA titrant is added to the sample plus indicator, the EDTA complexes metal ions. When enough EDTA has been added to complex all free metal ions in solution, the EDTA begins to remove the few remaining metal ions that are bound to the indicator, thus causing the indicator to undergo a color change just at the equivalence point. The indicator must bind the metal ions less strongly than the EDTA. Solutions for Complexometric Titrations Exercises 4. Two volumes of the EDTA solution will be needed for each volume of the Mn2+ solution so at the equivalence point the concentration of the MnY2- is given by At the equivalence point, assume that all of the Mn2+ and EDTA are initially complexed (as MnY2-), then dissociate according to: MnY2- º Mn2+ + EDTA init: 0.00333 M 0 0 equil: 0.00333 - x x x For Mn2+, Kf = 7.76 x 1013 and at pH = 7.00, αY4- = 3.8 x 10-4. x = 3.4 x 10-7 M = [Mn2+]

Solutions for Complexometric Tatrations Exercises

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