Complexometric Determination of Water Hardness Essay

AbstractThe piddle hardness for unknown pee hear number 40 was determined. From the results of the two complexometric titrations, the wet hardness of the unknown model was calculated to be 250.9 ppm CaCO3, which agrees with the ordinates of acceptable water hardness in the city of genus Phoenix and Tempe Arizona. IntroductionWhen rainfall picks up impurities from the soil, ions of sodium, magnesium, calcium, iron, and other metals are dissolved into the water. These impurities are what cause residues left on glassware from the reaction with the soap used for cleaning. urine hardness is from the metal ions with a +2 charge or higher being dissolved into the rainfall. When reporting water hardness, it is describe in units of mg CaCo3/L of solution, or in ppm due to one mg of solute having one millionth of the mass of a liter of water or dilute aqueous solution. It is reported using only CaCo3 because typically, Calcium is the largest contributor to the water hardness. The purpo se of this experiment was to determine the closeness of metal ion impurities in an unknown sample of hard water by performing a complexometric titration with EDTA. The results were then compared to the expected range for municipal water hardness from multiple city websites. MethodsAll procedures from the CHM 152 Lab, Complexometric Determination of weewee rigour (1) were followed precisely. Unknown water sample 40 was mixed with approximately 20 ml of DI water, 3.0 ml of Ammonia/Ammonium Chloride (NH(aq) Buffer pH=10), and 4 drops of Eriochrome minatory T indicator solution. It was then titrated with .004197 M EDTA, which was also made in the lab from 0.7582 g of , added to 500 mL of DI water, that was then standardized with a logical argument Calcium Ion Solution (CaCO(aq) 1.00g/1.00L) by titration. A total of 3 titration trials were completed to find the average meter of the EDTA, and the average water hardness of unknown water sample 40. Allmass measurements were taken from a AND Balance, serial number 12321601 and all titrations were done using a KIMAX buret, 173. Pipet measurements were taken from a 25mL Bel-Art, and 15mL Bel-Art pipet. The numeral techniques used in this experiment were, stoichiometry with jettye ratio for calculating the molarity of the EDTA solution and water hardness and relative average absolute deviation in ppt to show how closely the results from the Standardized EDTA titration of to each one trial agree with each other. Data AnalysisBased on the experiment and calculations, the average calculated concentration of metal ion impurities (water hardness) in unknown sample number 40 from this experiment was 250.9 ppm. From table 1, the average molarity of the titrated was calculated to be 0.004197 M. Table 1The molarity of the EDTA solution for each trial n was calculated as follows .0.01000 L CaCO3 SolnTotal EDTA Delivered L1.000 g CaCO31 L CaCO3 Soln1 mol CaCO3100.1 g CaCO31 mol Na2EDTA1 mol CaCO3=Molarity of Trial n The Ave rage Molarity of the EDTA solution was calculated as follows Average Molarity of EDTA Solution =Calculated molarity from each trialNumber of titration trials To determine how closely the results of each trial from the Standard Disodium EDTA titration (Table 1) agreed with each other, a relative average absolute deviation calculation was done. It was calculated as followsAbsolute deviation for trial n= Na2EDTA avg molarity-Total Na2EDTA Trial nabsolute deviations3Na2EDTA avg molarity1000=Estimated Prescision (ppt) The results of the above calculation came out to be 14.45 ppt. With the expected range of precision being at most five parts per thousand, it has been observed that the molarity of the standard Disodium EDTA solution includes some obvious error. It seems that the observation of color channel when Na2EDTA was titrated to the mixture of CaCO3, DI water, Eriochrome Black T, and ammonia/ammonium chloride was the most error prone. Not knowing when to stop titrating the EDTA sol ution, would have accounted for a misreading of measurement for the total plenty of EDTA solution added to complete the titration, making the final molarity for that trial less thanwhat was expected.Table 2Based on the molarity results from table 1 and the info from table 2, the average calculated water hardness of unknown water sample 40 was calculated to be 250.9 ppm CaCO3. The water hardness of unknown water sample 40 for each individual trial was calculated as follows=Total EDTA soln Delivered L0.02500 L CaCO3 soln0.004197 mol EDTA1 L EDTA soln1 mol CaCO31 mol EDTA100.1 g CaCO31 mol CaCO31000mg1.0 g Average Water Hardness (ppm)mg CaCO31 L CaCO3Interpretation of ResultsBased on the data, the calculated water hardness of the unknown sample number 40 (250.9 ppm), is within range of the city of Phoenixs calculated range of 164-291 ppm (2) and the city of Tempes calculate range of 150-400 ppm (3). References1. Complexometric Determination of Water Hardness, Procedures, Mesa Communi ty College CHM152LL website, http//www.physci.mc.maricopa.edu/Chemistry/CHM152/index.html, accessed 9/7/2013. 2. City of Phoenix website. http//phoenix.gov/waterservices/quality/index.html, accessed 9/8/2013. Copyright 2013 3. City of Tempe Az website. https//www.tempe.gov/index.aspx?page=1289Hardness, accessed 9/8/2013. Copyright