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Experiment 10 – The Chemistry of Natural WatersAlexandra RoquePartners: Matthew Roberts, Andrew Rust, Alireza SaatchiTA: Kayla GentileChem 113, Section 001November 17, 2017
I.Introduction: Water is the driving force behind planet Earth, without it life would be non-existent. Not only is water pivotal for the survival of all life, but also safe drinking water is just as important. It has been estimated that about 1 billion people are currently living with an insufficient amount of clean drinking water.1The impact of this global water crisis may not be felt to that degree in areas of the United States but other issues surrounding water quality are present. Understanding the biological and chemical properties of water and how it varies throughout individual water sources is important as consumers. Daily drinking water sources such as household taps, water bottles, and natural running water may contain high levels of dissolved minerals, specifically calcium and magnesium. The concentration of these cations, Ca2+ and Mg2+, in a sample can determine its chemical properties, referred to as hardness. Water hardness is measured by analyzing the quantity of these dissolved minerals in parts per million (ppm). When water contains a high concentration of Ca2+ and Mg2+it is considered hard, a low concentration is considered soft. 2 There are no legitimate health risks to hard water but it can become troublesome. Hard water can become problematic when mixed with soaps that are anions, producing a greasy scum that layers on top of an already cleaned area.Secondly, hard water will cause scale formation, deposits of calcite crystals (CaCO3), on the walls of industrial parts such as pipes and boilers that is costly to remove.2 A few ways to measure water hardness include techniques such as total dissolved solids(TDS), ethylenediaminetetraacetic acid (EDTA) titrationand atomic absorption spectrometry (AA). TDS is a qualitative analysis of measuring residue from a water sample, examining nonvolatile solids that are left after evaporation is initiated. EDTA titration is a quantitative analysis that measures total divalent cation content by performing a titration.2 This technique is performed using a chelating agent, in this case EDTA, 2
which possess a structure that allows for several bonds to form to a single metal ion.3EDTA titration is performed using an indicator (blue) at a high pH that reacts with Mg2+in the water sample, to form a color change (dark red.) Secondly, when the EDTA agent is added to the solution it will react with the Ca2+to form a colorless chelate2 Finally, the EDTA will then react with the Mg2+ and remove any cations from the indicator, returning solution to original color (blue.) Equation 1 below shows reaction that is taking place in EDTA titration2¿¿¿¿2¿¿2+¿EDTACaEDTA+MgEDTA+−¿HD¿+¿+Ca¿2+¿¿MgD¿+H¿2+¿+Ca¿¿HD¿+Mg¿(1)AA is an even more precise method of measuring water hardness that measures the amount of

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