Report 5 - EDTA Titration Determination of Mg2 CHM3120C-903...

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EDTA Titration: Determination of Mg2+CHM3120C-903Vincent Gallo U61917512Shane SpiersFebruary 29th2016
I. IntroductionA complexometric titration is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end of a titration. Complexometric titrations are particularly useful for the determination of a mixture of different metal ions in solution. Lewis acids and bases are commonly involved in this type of reaction. Most metal ions will react with electron pair donors to form complex ions, or chelates. A chelate is a compound containing a typically organic ligand bonded to a central metal at at two or more points. Ligands that can bond to an atom at more than one location are also known as multidentate ligands.Ethylenadiaminetetraacetic acid is a tertiary amine that is used regularly in the formation of chelates. EDTA has four acidic protons, therefore, the formation of metal-ion/EDTA complexes is dependent upon pH. The completion of the reaction requires that all of the EDTA will be in chelating form, which can be assured by buffering the reaction solution to a pH of 10. At this pH, EDTA is completely deprotonated, as seen below. This form of EDTA is known as the Y4- (chelating) form, and it is the negative charge on the four oxygen molecules that causes the attraction to metal ions such as Mg2+. It is important to note that the EDTA anion reacts with polyvalent metal cations in solution in a 1:1 stoichiometric ratio. Therefore, the number of moles of EDTA used will equal the number of moles of MgO in the unknown sample. The reaction procedes as follows: Mg2+(aq)+ EDTA-4(ag)[Mg(EDTA)]-2(aq)As the reaction progresses, the EDTA initially bonds with free Mg2+, which is colorless. Then, EDTA begins to bond with some MgIn complex. The indicator “In” is Eriochrom
Black T, which bonds with Mg2+to create a red color. EDTA has a stronger affinity for Mg2+ than does the indicator, so as EDTA is titrated into the solution, it replaces the indicator in the complex with Mg2+, changing the color of the solution from wine red to blue. This color change marks the end point of the titration. In this experiment, the percent mass of MgO in the unknown sample will be determined using titration techniques. If the experimental procedure is properly followed,and systematic error is avoided, then, the percent mass of MgO will be found with a percent error of less than .2% and there will be no significant difference between the variances of the two sets of trials.

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