Determination of Water Hardness Essay

doorwayIn this lab a total of six titrations are to be per readyed. Three of them will be done apply a know Ca2+ ancestor, (1.000 g CaCO3 /L root) and three of them will be done using an un cognise solution obtained from the stock room. The objective of this lab is to determine the badness of piddle, using the data collected from each titration performed with the unbeknownst(predicate) sample. Since the thinkosity of weewee arises from the presence of met wholeic element ions, we depose use disodium salt of EDTA and the indication Eriochrome bare T to determine the concentration of M 2+ ( Mg 2+ or Ca 2+) metallic element ion impurities.Chemical principle or theory involved in this labTo determine waters hardness we will use a technique called a chelometric titration. When a unbiassed molecule or anion (lewis base) donates electron pairs and attaches itself to a metal ion center (a Lewis acid), the resulting thud of atoms forms a single ion called a tortuous. When such complexes form the electron donating groups are called ligands. When ligands with more than one binding site form complexes with metal ions, we call this process chelation, where the ligand use is called a chelating agent. (lab manual) In this lab the chelating agent used is Na2EDTA. Our Indictor Eriochrome Black T, is a dye, 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 calcium ion solution, looks as follows Where H2In re leaves 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 + CaED TA 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(a) the fume hood and stir. Add 4 drops of the Eriochrome Black T indicator dye, then titrate with the disodim EDTA solution within 15 mins.At the endpoint the color changes from pink to violet to blue within 3-5 seconds. melodic phrase the volume of Na2EDTA that was used delivered from the burret, and repeat the titration 2 more times. Obtain an st ordinater water stock solution from the stock room taking watch of the transcendental number, then titrate with the standardized disodium EDTA solution Mix 25 mLs of the on the watch water sample with 20 mLs of deionized water, then unde r the fume hood, add 3 mLs of ammonium chloride buffer and stir. Add 4 drops of the Eriochrome Black T indicator dye, then titrate with the disodim EDTA solution within 15 bites 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 water sample test 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 CaC O3 1mol CaCO3 1mol Na2EDTA23.6 mL Na2EDTA 1 L CaCO3 100.1g 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 10-5 weewee hardness computeTrial 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 i n 2011 was in the range of 41- 330 ppm (http//www.3mwater.com/medi/documents/ WaterReport_GilbertAZ.pdf). This is a large range but is a range that my unknown water sample would fall within. According to Fairfax Water, a value everyplace 180 ppm is considered very hard, and according to the lab manual water with more than 200 ppm is considered hard. Based on this information I would fill up 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