The Analysis of Carbonate, Magnesium, and Copper by Three Separate Titrations: Weak Base, Metal-Ligand Complex, and Oxidation-Reduction Titrations

Joseph D. Hantho

Abstract


Many titrations depend upon an observable physical change, such as a change in color, for their endpoint to signify an equivalence point has been reached. There are a number of points during a titration where analysts can be misled prior to, at, or after an equivalence point has been reached without a visual aid for comparison. To that end, the analysis of carbonate by a weak base titration, magnesium by a metal-ligand complex titration, and copper by an oxidation-reduction titration were explored. Percent relative standard deviation (%RSD) and percent relative error (%RE) values were calculated for replicate measurements of the quality control (QC) standards. In addition, all three titration procedures were replicated with high-resolution color photographic documentation in an effort to attenuate the misdirection analysts often face due to the gradations of the observed changes near the endpoint. Generally, these gradations include how the analyte solution color appears before titration has begun, before the equivalence point, at the equivalence point, and after too much titrant has been added. Lastly, changes to the amount and type of water used in the metal-ligand complex titration of magnesium were also explored. By using 18 MW•cm at 25 °C deionized water instead of distilled water for every step of the procedure, there was a significant improvement in the clarity of the observed endpoint color change. This allowed for a significant increase in the precision and accuracy (in terms of %RSD and %RE) for the procedure when compared to the use of distilled water. This experiment is designed and is appropriate for an undergraduate quantitative analysis course.


Keywords


Weak Base, Metal-Ligand, Oxidation-Reduction, Titration

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