Complexometric determination of water hardness Essay

IntroductionThe purpose of this experiment is to determine the hardness of a sample of irrigate (89). Water hardness cigarette be evaluated by an acid-base neutralization titration. (When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt.) From the Bronsted-Lowry acid-base reaction theory, the H+ cation of the acid combines with the OH- anion of the base to form water. In this titration experiment, there are no definitive acidic or basic agents beingness evaluated. This requires the use of the Lewis acid-base theory.Instead of specify acid-base reactions in terms of protons or other bonded substances, the Lewis definition defines a base (referred to as a Lewis base) to be a compound that can donate an negatron pair, and an acid (a Lewis acid) to be a compound that can receive this electron pair. Similarly, in either type of acid-base neutralization experiment, an indicator is used to display when the source is neutra lized. The standardized Na2EDTA water resolving is will be titrated against the unk presentlyn water sample (89). Upon neutralization, the unknown water samples metal cation electrons will lurch to the Na2EDTA solution and will subsequently remove the sodium from the EDTA. ( unnoticeable 89)2+ + Na2EDTA (Unknown 89)EDTA + 2Na+Water hardness is expressed in in milligrams per liter.ProcedureThe first thing to be do was to manufacture the 0.004 M Na2EDTA solution. This was done by adding 0.7319 g Na2EDTA to approximately 500 mL of DI water. I obtained a 50.0mL burret, a 10.00 mL and a 25.00 mL impartation pipette, and the unknown sample (89) from the stockroom. The 50.0 mL burret was set in the burret stand. The Na2EDTA was in the burret and CaCO3 solution was in a 250 mL Erlenmeyer flask. The CaCO3 solution was comprised of 10.00 mL of 1.000g CaCO3/mL, approximately 30mL of DI water, 2.5 3.5 mL of fan (ammonia/ammonium chloride), and 4 drops of Eriochrome Black T indicator. Th e Na2EDTA was being titrated against the CaCO3 period simultaneously being mixed by a magnetic stir bar in the 250 mL Erlenmeyer flask. The titration was run to completion when theCaCO3 solution sullen from a violet to a blue color change.This was done three times for the standardization of the Na2EDTA. The titration for the now standardized Na2EDTA solution against the unknown water sample 89 follows a similar procedure as the first titration except the contents of the 250 mL differ. The Unknown sample solution was comprised of 25.00 mL of unknown, approximately 20 mL of DI water, 2.5 3.5 mL of buffer (ammonia/ammonium chloride), and 4 drops of Eriochrome Black T indicator. The Na2EDTA was being titrated against the Unknown while simultaneously being mixed by a magnetic stir bar in the 250 mL Erlenmeyer flask. The titration was run to completion when the unknown solution turned from a violet to a blue color change. This was done three times to determine the hardness of water sam ple 89.Experimental Data & countings1). Na2EDTA & CaCO3 titration.Na2EDTA solution0.7319 g & 500 mL DI WaterTrial 1CaCo3 SolutionNa2EDTA Solution10 mL 1.000g CaCO3/L31 mL DI waterV0 = 0.60 mL3.4 mL caramel brownVf = 25.20 mL4 drops IndicatorV = 24.60 mLTrial 210 mL 1.000g CaCO3/L30 mL DI waterV0 = 0.60 mL3.3 mL BufferVf = 23.92 mL4 drops IndicatorV = 23.22 mLTrial 310 mL 1.000g CaCO3/L30 mL DI waterV0 = 0.50 mL3.3 mL BufferVf = 24.23 mL4 drops IndicatorV = 23.73 mL2). Na2EDTA & Unknown water sample 89 titration.Trial 1Unknown SolutionNa2EDTA Solution25 mL Unknown sample20 mL DI waterV0 = 0.88 mL3.0 mL BufferVf = 13.80 mL4 drops IndicatorV = 12.92 mLTrial 225 mL Unknown sample21 mL DI waterV0 = 18.60 mL3.1 mL BufferVf = 30.80 mL4 drops IndicatorV = 12.20 mLTrial 325 mL Unknown sample20 mL DI waterV0 = 30.80 mL2.9 mL BufferVf = 43.20 mL4 drops IndicatorV = 12.20 mLNa2EDTA molarity equationNa2EDTA VNa2EDTA molarity wind 1 = 24.6 mL0.0040 MTrail 2 = 23.22 mL0.0042 MTrail 3 = 23.73 mL0 .0042 MNa2EDTA mean molarityAbsolute DeviationTrail 1 = 0.0001 M Na2EDTATrail 2 = 0.0001 M Na2EDTATrail 3 = 0.0001 M Na2EDTAEstimated precisionEstimated precision = 0.1 ppt.Calculating Water Hardness (parts per million)M mol Na2EDTA = Na2EDTAmean = 0.0041 MTrail 1 V = 12.92 mL = 216.4 ppmTrail 2 V = 12.20 mL= 204.3 ppmTrail 3 V = 12.20 mL= 207.7 ppmParts Per Million Mean Calculation DiscussionThere are two tangibles that I feel may have affected the results of my calculations. The first was being able to use the transfer pipet correctly. I recall two trials where there was a combination of having bubbles in the pipet and adding an excess of the limiting reagent. The other struggle for me in this lab was being able to effectively determine the reactions completion by color change. An unnecessary excess of NaEDTA may have been added to determine the reactions completion. These two pitfalls in my method can explain for the error in my work.For practical purpose, water hardness values l ess than 60 ppm is soft, while water with more than than 200 ppm is considered hard. The analysis of my unknown sample came out to be 209 ppm, a hard water sample. To present some validity to my result, I can before long compare the water hardnesss of my unknown water sample to the 1.000 g CaCO3. The CaCO3 solution has a hardness of 1000 ppm and my calculated unknown has a hardness of 209 ppm. Since the CaCO3 has a higher hardness value, this is why it took more Na2EDTA to neutralize it in the first sets of titrations. This assures me that my calculated result should be less than 1000 pmm.