Complexometric Determination of Water Hardness Essay Example for Free

Complexometric Determination of Water Hardness EssayWhen a polyatomic ligand with multiple lone pairs of electrons available for bonding to a central metal ion forms a complex with a metal ion, a process cognize as chelation takes place. Metal ion impurities bottom of the inning be found by using disodium salt of EDTA to determine the concentration of M2+ by complexometric or chelometric titration. Erichrome Black T makes it easy to see when the EDTA has completely chelated the metal impurities. When the metal cation is politic present in the water, the antecedent will be a complex with a pink tint. once enough EDTA has been sumed to the M2+ solution the metal ions complex to the EDTA leaving the indicator solvated causing a color change from pink to blue. Once the color has changed to blue, the titration has reached an end point and the M2+ metal ion impurities in hard water can be calculated. ProcedurePrepare 500 mL of 0.004 M disodium EDTA solution by dissolving 0.7-0. 8g of Na2EDTA in 500 mL deionized water. Standardize the solution by using a 10 mL transfer pipet to add 10 mL of regulate calcium ion stock solution to a 250 mL Erlenmeyer flask and mixing it with 30 mL of deionized water. Add 3 mL of ammonia/ammonium chloride buffer (pH 10) to ensure that the calcium ions remain in the solution for accurate results. Add four drops of Eriochrome Black T indicator solution so that a color change can be visible during titration. Once the solution is prepared, titrate it with the disodium EDTA solution. Add the solution quickly at first and once the color changes from pink to reddish blue slow down the titration until the color changes from violet to blue. Then record the results.Part 2 UnknownAfter receiving an unknown prepared water strain record the unknown in your lab notebook (unknown 76). After the unknown has been recorded, transfer 25 mL of the sample into a 250 mL Erlenmeyer flask with 20 mL of DI water. As in part one, add 3 mL of ammonia /ammonium chloride buffer (pH10) to the solution along with four drops of Erichrome Black T indicator. Once the solution has been made, titrate the solution with the standardized disodium EDTA solution and calculate the hardness of the prepared water sample from the titration. Compare the results to the expected range for municipal water hardness on your citys water quality lab website.DataTest 1 Standardization of EDTAMass of CaCO3 0.01 gMoles of CaCO3 9.910-5Molarity of the 250 mL standard Ca2+ 3.9610-4 MColumn1 Trial 1 Trial 2 Trial 3Volume of Ca2 Titrated (mL) 10 10 10Moles Ca2+ Titrated 9.910-5 9.910-5 9.910-5Moles EDTA 9.910-5 9.910-5 9.910-5Initial Buret reading (mL) 1 1 1 final examination burette reading (mL) 26.3 26.5 27Volume of EDTA (mL) 25.3 25.5 26Molarity of EDTA (M) 0.0039 0.0039 0.0038Average Molarity of EDTA 0.0039 M Test 2 Unknown Determination Sample 76Column1 Trial 1 Trial 2 Trial 3Volume of Water Sample Used (mL) 25 25 25Initial buret reading (mL) 1 1 1Final buret reading (mL) 14.8 15 14.9Volume of EDTA used (mL) 13.8 14 13.9Moles EDTA 5.3810-5 5.4610-5 5.4210-5Moles Ca2+ in sample 5.3810-5 5.3810-5 5.3810-5 Moles Ca2+ per litre 5.3810-4 5.3810-4 5.3810-4 Grams CaCO3 per liter 0.054 0.055 0.055Water hardness 29.73 30.61 30.17Average water hardness (ppm CaCO3) 30.17 CalculationsTest 1Calculate Mass of CaCO3 used in the reaction10 mL Ca2x 1L/1000mLx 1g/1L= 0.01 g CaCO3Calculate Moles of CaCO30.01 g CaCO3x 1bulwark CaCO3/100.1 g CaCO3= 9.910-5 counterspyesCaCO3Molarity of 250 mL of standard Ca2+ solution9.910-5 moles CaCO3/0.250 L= 3.9610-4 M Ca2+MolesMoles of EDTAMoles of EDTA=Moles CaCO3, 1 to 1 ratio.Molarity of EDTATrial 1(10 mL CaCO3 sol/25.6 mL EDTA end point)x (1L CaCO3 Sol/1000mL CaCO3 sol)x(1 g CaCO3/1 L sol)x(1 mole CaCO3/100.1g CaCO3)x(1 mole EDTA/1 mole CaCO3)x(1000 mL EDTA sol/1 L EDTA sol) = 0.0039 M Trial 2(10 mL CaCO3 sol/25.5 mL EDTA end point)x (1L CaCO3 Sol/1000mL CaCO3 sol)x(1 g CaCO3/1 L sol)x(1 mole CaCO3 /100.1g CaCO3)x(1 mole EDTA/1 mole CaCO3)x(1000 mL EDTA sol/1 L EDTA sol) =0.0039 M Trial 3(10 mL CaCO3 sol/26 mL EDTA end point)x (1L CaCO3 Sol/1000mL CaCO3 sol)x(1 g CaCO3/1 L sol)x(1 mole CaCO3/100.1g CaCO3)x(1 mole EDTA/1 mole CaCO3)x(1000 mL EDTA sol/1 L EDTA sol) =0.0038 MAverage Molarity(0.0039 M+0.0039 M+0.0039 M)/3=0.0039 MTest 2Calculate moles of EDTATrial 10.0138 L EDTA(3.910-3 moles EDTA)= 5.8310-5 Moles EDTATrial 20.014 L EDTA(3.910-3 moles EDTA)= 5.4610-5 Moles EDTATrial 30.0139 L EDTA(3.910-3 moles EDTA)= 5.4210-5 Moles EDTAMoles Ca2+Moles of Ca2+ equals moles of EDTAMoles of CA2+ per literMoles Ca2+ x 10 to get Moles per leterTrial 15.8310-5 Moles EDTA(10)= 5.3810-4 Moles Ca2+ per LiterTrial 25.4610-5 Moles EDTA(10)= 5.4610-4 Moles Ca2+ per LiterTrial 35.4210-5 Moles EDTA(10)= 5.4210-4 Moles Ca2+ per LiterGrams CaCO3 per literCalculate by multiplying moles of Ca2+ by grams per mole of Ca2+Trial 1(5.3810-4 Moles Ca2+/ 1L)(101.1g/1mole)= 0.054g/L CaCO3Trial 2(5.4610-4 Moles Ca2+ /1L) (101.1g/1mole)= 0.055g/L CaCO3Trial 3(5.4210-4 Moles Ca2+ /1L) (101.1g/1mole)= 0.055g/L CaCO3Water HardnessTrial 1(13.8 mL EDTA/25 mL sample)(1 L EDTA sol/1000 mL EDTA)(5.3810-4 mol EDTA/1L EDTA)(1 mol CaCO3/1 mol EDTA)(100.1g CaCO3/1 mol CaCO3)(1000mg CaCO3/1g CaCO3)(1000mL Sample sol/1L sample sol)= 29.73 ppm CaCO3 Trial 2(14 mL EDTA/25 mL sample)(1 L EDTA sol/1000 mL EDTA)(5.4610-4 mol EDTA/1L EDTA)(1 mol CaCO3/1 mol EDTA)(100.1g CaCO3/1 mol CaCO3)(1000mg CaCO3/1g CaCO3)(1000mL Sample sol/1L sample sol)= 30.61 ppm CaCO3Trial 3(13.9 mL EDTA/25 mL sample)(1 L EDTA sol/1000 mL EDTA)(5.4210-4 mol EDTA/1L EDTA)(1 mol CaCO3/1 mol EDTA)(100.1g CaCO3/1 mol CaCO3)(1000mg CaCO3/1g CaCO3)(1000mL Sample sol/1L sample sol)= 30.17 ppm CaCO3Average water hardness(29.73+30.61+30.17)/3= 30.17 ppm CaCO3ConclusionThe water hardness of a known and unknown sample solution has been determined by means of titration with disodium salt of EDTA to calculate the concentration of M2+ metal ion impurities in hard water in a process known as chelation. After running tests and calculating the water hardness in an unknown sample it was found that there was 30.17 ppm CaCO3 in the sample.