Determination of Total Hardness of Water Samples

Topics: Hard water, Calcium, Water Pages: 4 (1243 words) Published: August 31, 2013
Determination of Total Hardness of Water Samples

Ana Margarita Y. Austria, Shane R. Frigillana, Patricia Alyssa P. Manapul BS Chemistry III
August 25, 2012
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Abstract
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This experiment aims to determine the hardness of a water sample. The method used is, complexometric titration. This process took use of the standardized EDTA solution (for EDTA is not a primary standard) with CaCO3 and the indicator Eriochrome Black T which reacts with the titrant (EDTA) and the metal ion in the solution, thus, creating a change in color (blue) of the solution. The result recorded for the standardization of the EDTA solution has the mean molarity of 0.0773 ± 0.0003 M. In expressing the hardness of the water, it is often in terms of ppm or “parts per million” of CaCO3 in the sample. This is because, Ca2+ and Mg2+ were often the present ions in a water, that majorly causes for its heaviness. In this experiment, the calculated ppm of CaCO3 of the water sample from Sta. Cruz Maynilad is 76.05 ± 3.38. This is still under the category of a soft water, for the condition: < 100 ppm – soft. -------------------------------------------------

Introduction
Complexometric titration is one of the best ways of measuring total water hardness. At pH, around 10, EDTA easily reacts with both calcium and magnesium in the same molar ratio (1:1). Stability constant of calcium complex is a little bit higher, so calcium reacts first, magnesium later. In this experiment a solution of EDTA will be standardize by titration against a standard solution made from calcium carbonate, CaCO3. The EDTA solution can then be used to determine the hardness of an unknown water sample. Since both EDTA and Ca2+ are colorless, it is necessary to use a special indicator to detect the end point of the titration. The indicator most often used is called Eriochrome Black T, which forms a very stable wine-red...

References: Harvey, David (2000). Modern Analytical Chemistry. The McGraw-Hill Companies, United States of America.
Skoog, Douglas, et. al. (1996). Fundamentals of Analytical Chemistry (7th ed). Saunders College Publishing, West Philadelphia, USA.
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