Determination of Water Hardness Essay

IntroductionIn this lab a total of six titrations are to be per solveed. Three of them will be done use a known Ca2+ solution, (1.000 g CaCO3 /L solution) and three of them will be done using an unknown solution obtained from the stock room. The objective of this lab is to look out the hardness of peeing, using the data collected from each titration performed with the unknown sample. Since the hardness of water arises from the presence of metal ions, we muckle use disodium salt of EDTA and the index Eriochrome dispirited T to determine the concentration of M 2+ ( Mg 2+ or Ca 2+) metal ion impurities.Chemical principle or conjecture involved in this labTo determine waters hardness we will use a technique called a chelometric titration. When a neutral molecule or anion (lewis base) donates electron pairs and attaches itself to a metal ion center (a Lewis acid), the resulting cluster of atoms forms a single ion called a complex. When such complexes form the electron donating grou ps are called ligands. When ligands with much than one bind site form complexes with metal ions, we call this process chelation, where the ligand used is called a chelating agent. (lab manual) In this lab the chelating agent used is Na2EDTA. Our Indictor Eriochrome Black T, is a soil, and will form a pink complex in the presence of a metal cation. As EDTA solution is added to the solution, the metal ions will complex to the EDTA solution leaving the indicator solvated. The chemical equation, with the known atomic number 20 ion solution, looks as follows Where H2In represents the solvated indicator Erichrome Black T dye.H2In + Ca 2+ CaIn + 2H(blue) (pink)As EDTA is added to the solution, it grabs the Ca ions away from the Erichrome Black T dye molecules to form a more stable complex. When solvated, and alone in the solution, the Erichrome Black T dye will produce a blue color it can be represented by the equation belowEDTA 4 + CaIn + 2H H2In + CaEDTA 2(pink) (blue)Procedure or MethodFirst prepare your disodium EDTA solution by weighing out 0.7- 0.8 grams of Na2EDTA and dissolve it in 500 mLs of deionized water. Place in a sealed container and shake vigorously. Standardize the Na2EDTA solution using calcium ion stock solution Add 10 mL of calcium solution to a flask, and add 30 mLs of deionized water. Add 3 mLs of ammonium chloride buffer under the fume hood and stir. Add 4 drops of the Eriochrome Black T indicator dye, then measure with the disodim EDTA solution inwardly 15 mins.At the endpoint the color changes from pink to violet to blue within 3-5 seconds. Note the volume of Na2EDTA that was used delivered from the burret, and repeat the titration 2 more times. Obtain an unknown water stock solution from the stock room taking note of the unknown number, then titrate with the standardized disodium EDTA solution unify 25 mLs of the prepared water sample with 20 mLs of deionized water, then under the fume hood, add 3 mLs of ammonium chloride buffer a nd stir. Add 4 drops of the Eriochrome Black T indicator dye, then titrate with the disodim EDTA solution within 15 minutes Repeat the titration 2 more times, and calculate the hardness of the prepared water sample from each of the titrations.Observations and CalculationsAmount of Na2EDTA solution Amount of Na2EDTA solution required to titrate calcium Ion solution required to titrate unknown H2O sample struggle 1 25.0 mL15.7 mLTrail 2 23.8 mL14.9 mLTrial 3 23.6 mL15.5 mLBecause EDTA chelates Ca 2+ ions in a one-to-one molar ratio we can calculate the moles present of Na2EDTA using the following formula(s)Trial 1Na2EDTA = 10.00 mL CaCO3 1.000 g CaCO3 1mol CaCO3 1mol Na2EDTA25.0 mL Na2EDTA 1 L CaCO3 100.1g CaCO3 1 mol CaCO3 =.004 moles Na2EDTATrial 2Na2EDTA = 10.00 mL CaCO3 1.000 g CaCO3 1mol CaCO3 1mol Na2EDTA23.8 mL Na2EDTA 1 L CaCO3 100.1g CaCO3 1 mol CaCO3 =.004197 moles Na2EDTATrial 3Na2EDTA = 10.00mL CaCO3 1.000 g CaCO3 1mol CaCO3 1mol Na2EDTA23.6 mL Na2EDTA 1 L CaCO3 1 00.1g CaCO3 1mol CaCO3 =.004233 moles Na2EDTAMean of all 3 trials = .004 + .004197 + .004233 / 3 = .004143Absolute deviation Estimated Precision(ppt)Trial 1 .004143 .004 = 1.43 x 10-4 .02229 X 1000 = 23.09 ppt .004143 Trial 2 .004143 .004197 = -5.4 x 10-5Trial 3 .004143 .004233 = -9 x 10-5H2O hardness figureTrial 1 15.7 mL Na2EDTA X .004143mol Na2EDTA X 1mol CaCO3 X 100.1g CaCO30.02500 L CaCO3 1L Na2EDTA 1mol Na2EDTA 1mol CaCO3Trial 1 H2O hardness = 260.44 ppmTrial 2 14.9 mL Na2EDTA X .004143mol Na2EDTA X 1mol CaCO3 X 100.1g CaCO30.02500 L CaCO3 1L Na2EDTA 1mol Na2EDTA 1mol CaCO3Trial 2 H2O hardness = 247.17 ppmTrial 1 15.5 mL Na2EDTA X .004143mol Na2EDTA X 1mol CaCO3 X 100.1g CaCO30.02500 L CaCO3 1L Na2EDTA 1mol Na2EDTA 1mol CaCO3Trial 3 H2O hardness = 257.12 ppmAverage H2O hardness for unknown 127 = 254.91 ppmConclusionThe average water hardness for unknown 127 is 254.91 ppm. City of Gilberts average water hardness in 2011 was in the range of 41- 330 ppm (http//www.3mwater.co m/medi/documents/ WaterReport_GilbertAZ.pdf). This is a large range but is a range that my unknown water sample would fall within. jibe to Fairfax Water, a value over 180 ppm is considered very hard, and according to the lab manual water with more than 200 ppm is considered hard. Based on this breeding I would conclude that my unknown water sample has a high amount of metal ions present.ReferencesLab ManualCity of Gilbert, http//www.3mwater.com/medi/documents/WaterReport_GilbertAZ.pdfFairFax Water, http//www.fcwa.org/water/hardness.htm