Experiment 10: The Chemistry Of Natural Waters

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Experiment 10: The Chemistry of Natural Waters Kristen Vito Partners: Brandon Weiss, Matt Verne, Shrudhi Venkad Chemistry 111 Section 104 TA: Ryan O’Neill 11/11/14 Introduction Water is one of the most valuable substances on the planet. It is used in a variety of economic and industrial practices, as well as within households for everyday activities such as cooking, cleaning and more. The composition of this “everyday” water is tainted by the presence of ions, often acquired from atmospheric gases and materials from soils and rocks, like dolomite and limestone. “Hardness” is the term most often used to evaluate some of water’s imperfections. Water hardness can be defined as the amount of the dissolved divalent cations or species with…show more content…
Each member of the group obtained their samples individually and carried out procedures to determine the hardness of their sample. After these procedures were completed, values were shared with in the group in order to form conclusions. The first part of this experiment was Atomic Absorption Spectroscopy. Samples were placed into two large pipets with removed stems. One pipet is used to determine magnesium concentration and the other is used to determine calcium concentration. The tap water samples were diluted in order to obtain an accurate reading while the water bottle remained untouched. The samples were then analyzed using the AA instrument. The values obtained in this part of the procedure were later used to determine hardness. In the next steps, the TDS method was used to evaluate samples. A drop of the water sample under observation, a drop of 1 x 10^-3 M Ca2+ and a drop of distilled water were placed upon a small piece of aluminum foil and heated on a hot plate. After the solutions were dissolved the residue left behind on the piece of foil was observed and recorded in lab…show more content…
With these numbers a liner relationship was denoted. The equation for this linear relationship was used to calculate the hardness of the samples analyzed by AA. Using the equation y=0.0069x+0.0078 the concentration of Calcium ions was determined by solving for the x value. Magnesium concentration was determined by the se of the same method. The hardness calculated by each group member is as follows Table 1: Overall Concentrations Great Value Bottled Water South Halls East Halls Pollock Halls AA-Concentration of Calcium and Magnesium ions (ppm) 1.665 ppm 170.5 ppm 347.9 ppm 291 ppm EDTA-Concentration of all 2+ ions 60 ppm 160 ppm 320 ppm 200 ppm Sample Calculation: Using the formulas displayed on the graphs above and the values given by the AA instrument hardness was calculated. Calcium Concentration: AA Analysis y=0.0069x+0.0078 0.0124=0.0069x+0.0078 x=0.666 ppm Ca 0.666ppm Ca2+ x (100CaCO3/1 mole)= 1.665 ppm hardness EDTA M 1V 1=M 2V 2 (2.0x10^-4)(3 drops)=M 2(1 drop)=6.0x10^-4 M Conversion to ppm 6.0x10^-4 M/1 liter of solution x 100g of sample/1 mole x100g of sample/1 mole = 60

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