The H2O hardness for unknown H2O sample figure 40 was determined. From the consequences of the two complexometric titrations. the H2O hardness of the unknown sample was calculated to be 250. 9 ppm CaCO3. which agrees with the scopes of acceptable H2O hardness in the metropolis of Phoenix and Tempe Arizona. Introduction

When rainfall picks up drosss from the dirt. ions of Na. Mg. Ca. Fe. and other metals are dissolved into the H2O. These drosss are what cause residues left on glasswork from the reaction with the soap used for cleansing. Water hardness is from the metal ions with a +2 charge or higher being dissolved into the rainfall. When describing H2O hardness. it is reported in units of mg CaCo3/L of solution. or in ppm due to one milligram of solute holding one millionth of the mass of a litre of H2O or dilute aqueous solution. It is reported utilizing merely CaCo3 because typically. Calcium is the largest subscriber to the H2O hardness. The intent of this experiment was to find the concentration of metal ion drosss in an unknown sample of difficult H2O by executing a complexometric titration with EDTA. The consequences were so compared to the expected scope for municipal H2O hardness from multiple metropolis web sites. Methods

All processs from the CHM 152 Lab. Complexometric Determination of Water Hardness ( 1 ) were followed exactly. Unknown H2O sample # 40 was assorted with about 20 milliliters of DI H2O. 3. 0 milliliter of Ammonia/Ammonium Chloride ( NH ( aq ) Buffer pH=10 ) . and 4 beads of Eriochrome Black T index solution. It was so titrated with. 004197 M EDTA. which was besides made in the lab from 0. 7582 g of. added to 500 milliliter of DI H2O. that was so standardized with a stock Calcium Ion Solution ( CaCO ( aq ) 1. 00g/1. 00L ) by titration. A sum of 3 titration tests were completed to happen the mean molar concentration of the EDTA. and the mean H2O hardness of unknown H2O sample # 40. All
mass measurings were taken from a AND Balance. consecutive figure 12321601 and all titrations were done utilizing a KIMAX buret. # 173. Pipet measurings were taken from a 25mL Bel-Art. and 15mL Bel-Art pipet. The numerical techniques used in this experiment were. stoichiometry with mole ratio for ciphering the molar concentration of the EDTA solution and H2O hardness and comparative mean absolute divergence in ppt to demo how closely the consequences from the Standardized EDTA titration of each test agree with each other. Datas Analysis

Based on the experiment and computations. the mean deliberate concentration of metal ion drosss ( H2O hardness ) in unknown sample figure 40 from this experiment was 250. 9 ppm. From table 1. the mean molar concentration of the titrated was calculated to be 0. 004197 M. Table 1

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The molar concentration of the EDTA solution for each test N was calculated as follows: . 0. 01000 L CaCO3 SolnTotal EDTA Delivered L?1. 000 g CaCO31 L CaCO3 Soln?1 mol CaCO3100. 1 g CaCO3?1 mol Na2EDTA1 mol CaCO3=Molarity of Trial n The Average Molarity of the EDTA solution was calculated as follows: Average Molarity of EDTA Solution =Calculated molar concentration from each trialNumber of titration tests To find how closely the consequences of each test from the Standard Disodium EDTA titration ( Table 1 ) agreed with each other. a comparative mean absolute divergence computation was done. It was calculated as follows:

Absolute divergence for test n= Na2EDTA avg molarity-Total Na2EDTA Trial N
absolute deviations3Na2EDTA avg molarity?1000=Estimated Prescision ( ppt ) The consequences of the above computation came out to be 14. 45 ppt. With the expected scope of preciseness being at most five parts per 1000. it has been observed that the molar concentration of the standard Disodium EDTA solution includes some obvious mistake. It seems that the observation of colour alteration when Na2EDTA was titrated to the mixture of CaCO3. DI H2O. Eriochrome Black T. and ammonia/ammonium chloride was the most error prone. Not cognizing when to halt titrating the EDTA solution. would hold accounted for a misreading of measuring for the entire volume of EDTA solution added to finish the titration. doing the concluding molar concentration for that test less than
what was expected.

Table 2

Based on the molar concentration consequences from table 1 and the informations from table 2. the norm calculated H2O hardness of unknown H2O sample 40 was calculated to be 250. 9 ppm CaCO3. The H2O hardness of unknown H2O sample 40 for each single test was calculated as follows:

=Total EDTA soln Delivered L0. 02500 L CaCO3 soln?0. 004197 mol EDTA1 L EDTA soln?1 mol CaCO31 mol EDTA?100. 1 g CaCO31 mol CaCO3?1000mg1. 0 g Average Water Hardness ( ppm ) ?mg CaCO31 L CaCO3
Interpretation of Consequences
Based on the information. the deliberate H2O hardness of the unknown sample figure 40 ( 250. 9 ppm ) . is within scope of the metropolis of Phoenix’s calculated scope of 164-291 ppm ( 2 ) and the metropolis of Tempe’s calculate scope of 150-400 ppm ( 3 ) . Mentions

1. Complexometric Determination of Water Hardness. Procedures. Mesa Community College CHM152LL web site. hypertext transfer protocol: //www. physci. megahertz. Maricopa. edu/Chemistry/CHM152/index. hypertext markup language. accessed 9/7/2013. 2. City of Phoenix web site. hypertext transfer protocol: //phoenix. gov/waterservices/quality/index. hypertext markup language. accessed 9/8/2013. Copyright 2013 3. City of Tempe Az web site. hypertext transfer protocol: //www. tempe. gov/index. aspx? page=1289 # Hardness. accessed 9/8/2013. Copyright


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