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Yealy 1The Chemistry of Natural WatersCourtney YealyChemistry 111Section 106November 12, 2009Group Members: Brittany Walker, Jaime Underkloffer, Courtney YealyTA: Trung TruongIntroduction:
Yealy 2Water is one of the most basic necessities for life and serves a copious amount of uses in our daily lives. Water hardness is one factor that can limit the utility of water. Water hardness refers to the concentration of divalent calcium and magnesium cations in a water sample. Though most natural waters contain additional hardness ions such as lead and iron , they are usually present in insignificant concentrations concerning the hardness . Industrial and domestic water users are concerned about the hardness of their water because as the hardness of water increases, scaling increases on industrial equipment and boilers . These calcite crystals that make up scale formations are extremely expensive to remove , and hard water in homes requires more soap and detergent to create lather . The hardness of water can be measured in several ways.One way to determine hardness is by ethylenediamine tetraacetic acid (EDTA) titration. EDTA titration is used to determine the divalent cations present in a sample of water (3). EDTA is a chelating agent that when combined with Eriochrome Black T (EBT) dye will cause a color change in the presence of calcium and magnesium ions . A different way to measure hardness is by Atomic Absorption Spectrophotometry (AA). This method is used to determine the metals that are dissolved in a solution. Monochromaticlight of the same energy as the metal ion is projected through the water sample which is aspirated over a flame. The amount of light absorbed by the sample is detected by use of a monochrometer and a photomultiplier tube (PMT), in order to determine the presence of the metal by assessing the
Yealy 3decrease in wavelength . The Atomic absorption method only identifies one metal while EDTA titration assesses all the divalent cations in a water sample. The EDTA titration is a more subjective method, while AA produces more precise results.In order to reduce the hardness of water, several methods can be used such as divalent cation removal or by use of a water softener. Softening techniques work by removing or replacing the divalent cations. Cation resin exchange works by removing the cations from water samples by means of ion exchange. Monovalent cations, in this case H+ions, are exchanged with the divalent ions. This is usually carried out by percolating water through a column that contains the monovalent ions in order to exchange them for the divalent cations such as Ca2+. For this experiment, samples were taken from a branch of the Conewago Creek in New Oxford, PA , a residential well in Reedsville, PA , and the bathroom tap of McKee Hall, University Park, PA . Tap water was predicted to be the hardest sample, and Conewago Creek water the least hard. Well water was predicted to have a moderate hardness compared