Natural Waters Lab Report.docx - The Chemistry of Natural...

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The Chemistry of Natural Waters and their Hardness Name: Taylor Bickel Date: November 7, 2019 Class: Chemistry 113 Section 001 Group Members: Sophia Bianchi and Devon Baughan TA: Kyra Murrell
Introduction: Water makes up 60% of the human body (4). According to USGS, water hardness is characterized as the amount of dissolved calcium and magnesium in the water (3). Hardness can be the result of compounds of calcium, magnesium, and a variety of other metals (3). Water hardness is not a health concern but it can still be a problem (3). Hard water has a tendency to cause mineral buildup in plumbing, fixtures, and water heaters. These problems can result in damaged equipment (3). For example, the buildup can lead to pipes to becoming closed up, which can prevent water movement through that pipe and decrease water pressure. Water has an abundance of internal components. Primarily water consists of Ca 2+ and Mg 2+ ions as well as the counter ions being bicarbonate and sulfate. The solubility of these ions can be increased by the acidity of aqueous solutions of carbon dioxide. For example, groundwater can have a very high acidity due to the fact that large amounts of carbon dioxide can be produced by biological activity (1). The easiest procedure that can be utilized in order to find out what solutes are present in a particular water sample is to examine the sample, after evaporation. This method is simple because drops of the samples are simply placed on a heating pad and evaporated in order to examine the residue of nonvolatile solids that remain. The residue that is left is called the total dissolved solids (TDS). This method is a qualitative step that allows for the experimenter to make observations of the leftover residue. One of the quantitative steps that will be used in the experiment will be to find the total divalent cation content of a particular sample using Ethylenediaminetetraacetic acid (EDTA) complexation titrations (7). EDTA is used for solubility reasons alongside of the use of an indicator, eriochrome black T (EBT). This indicator has the ability to form colored chelates with particular metal ions, Mg 2+ , but not with Ca 2+ (1). Another quantitative method that will be used is atomic absorption (AA), in order to
determine what metals are dissolved or suspended in the water sample (1). AA testing involves the sample being atomized in a flame and absorbing the ultraviolet light which allows for the free atoms to go through electronic transitions from a ground state to an excited state (6). AA analyzes specific ions in the different water samples. This method is the most expensive because of how extravagant the spectrophotometer is. The amount of absorbance is proportional to the concentration of the metal atoms in the sample (1). In order to figure out the unknown concentration of metal concentration within a sample, the Beer-Lambert law is used. The Beer- Lambert law is I t = I 0 (10 -abc ). This law works parallel to finding atomic absorbance because the

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