Chemistry Of Natural Waters Essay

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Exp. 10 - The Chemistry of Natural Waters
David Graves
CHEM 111 Section 104
TA: Lai Shi
Group Members: Jasmine Graves, Brad Hensler, Peter Hoholick


Experiment 10: The Chemistry of Natural Waters investigates the topic known as water hardness. Hardness is a chemical property of water that evaluates the concentration of dissolved divalent cations such as Ca and Mg, which happen to be the two ions that are tested for in the experiment. Hardness can be measured in multiple ways such as molarity (M) or parts per million (ppm).
Since all natural waters contain ion concentrations of dissolved minerals, it is important to known the hardness value because hard water can cause scale formation in industrial
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Numerous tests have been created to measure the magnitude of said concentrations. The tests range from simply evaporating the solvent and examining the leftover nonvolatile residue that remains, which is known as the total dissolved solids (TDS) of the sample, to chemical titrations using indicators (EDTA), to advanced spectroscopy of the sample using emission spectrums to determine ion absorbance values (AA Spectroscopy). There are a few differences between AA Spectroscopy and EDTA titrations when it comes to determining water hardness as both tests use different techniques. AA Spectroscopy is used to determine the concentration of metal ions in a water sample. A spectrophotometer is used to read the absorbance value of the cations in a flame that emits a photon read by the machine. Different elements will emit different lengths of photons which in turn produces an absorbance value. The absorbance values are then plotted on a calibration graph to determine the unknown concentration. EDTA titrations require much less equipment since it is more of a chemical test. An indicator EBT is added to a known volume of your water sample and should turn blue. Then, the indicator reacts with the Mg ions in the sample to turn to a pinkish-red

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