Water Hardness Essay Example for Free

Water Hardness Essay METHODS: 1. Prepare an approximate 0.004 M disodium EDTA solution. To prepare this solution, weigh about 0.7-0.8 g of Na2EDTA and dissolve in 500 mL deionized water in your plastic bottle. Make to to shake the bottle to dissolve the salt. 2. Obtain a 250-mL Erlenmeyer flask and transfer a 10 mL of CaCO3 using a buret into the flask. 3. Measure 30 mL of deionized water and add it into the titration flask. 4. Make sure to stir the solution 5. Inside a fume hood, add 3mL of ammonia/ammonium chloride buffer (pH10) into the flask and stir for another 30 seconds. 6. Add four drops of Eriorchrome Black T indicator solution. Stir for another 30 seconds 7. Begin titration. Record your initial volume and final volume. At the endpoint, the color will change to pink to violet to blue. 8. Repeat this titration two more times. Now that you recorded the volume, your second and third trial should be a lot easier. 9. Take your water sample that you obtain from the stockroom and record the unknown number. 10. Transfer 25 mL of the unknown water sample to a 250-mL Erlenmeyer flask. 11. Add about 20 mL of deionized water to the titration flask. Stir for 30 seconds 12. Inside a fume hood, add about 3 mL of ammonia/ammonium chloride buffer (pH10) and stir for another 30 seconds. 13. Add four drops of Eriorchrome Black T indicator solution to your flask and stir for 30 seconds. 14. Begin titrating. Record you initial volume and final volume. Repeat this twice more. Calculate the average hardness and your experimental precision from the three trials. RESULTS: EDTA Solution: 0.7533g of Na2EDTA mixed with 500ml DI water Table A: Standardization of EDTA Trial| Start Volume| End Volume| Amount of EDTA| 1| 3.90ml| 29.85ml| 25.95ml| 2| 5.35ml| 28.35ml| 23.00ml| 3| 0.45ml| 23.50ml| 23.05ml| Moles EDTA calculations 1st and 3rd trial (10.1 mL CaCO3) x (1L/1000ml) x 1.000g CaCO3/1L) x (1 mole CaCO3/100.1 g CaCO3) x (1 mole EDTA / 1 mole CaCO3) x (1000ml/L) = 0.101moles EDTA/L 2nd trial (9.90 ml CaCO3) x (1L/1000mL) x (1.00 g CaCO3/L) x (1 mole CaCO3/100.1g CaCO3) x (1 mole EDTA/1 mole CaCO3)x (1000 mL/1L) == 0.099 moles EDTA/L Mean molarity: (0.101 + 0.099 + 0.101)/3 = 0.100 moles EDTA / L Water hardness calculations Unknown water sample #24 Table 2. Water sample Trial| EDTA | Water sample #24| 1| 13.45ml| 25.1ml| 2| 13.35ml| 25.5ml| 3| 13.50ml| 25.0ml| CaCO3 molar mass: 100.1g/mole 1st trial (13.45 mL EDTA/25 mL of unknown water sample) x (1L/1000mL) x (0.101 moles EDTA/1L) x (1mole CaCO3/1 mole EDTA) x (100.1 g CaCO3/1 mole) x (1000 mg CaCO3/1g) x (1000mL/1L) == 5439.2 mg CaCO3/1L 2nd trial (13.35 mL EDTA/25 mL of unknown water sample) x (1L/1000mL) x (0.099 moles EDTA/1L) x (1mole CaCO3/1 mole EDTA) x (100.1 g CaCO3/1 mole) x (1000 mg CaCO3/1g) x (1000mL/1L) == 5291.9 mg CaCO3/1L 3rd trial (13.50 mL EDTA/25 mL of unknown water sample) x (1L/1000mL) x (0.101 moles EDTA/1L) x (1mole CaCO3/1 mole EDTA) x (100.1 g CaCO3/1 mole) x (1000 mg CaCO3/1g) x (1000mL/1L) == 5459.5 mg CaCO3/1L Calculate the total hardness in ppm CaCO3 1st trial 13.45ml EDTA x (0.004M/1000ml) x (100.1g CaCO3/1mole CaCO3) x (1000mg CaCO3/1g CaCO3) x (1000L/25.1ml) = 214.6 ppm CaCO3 2nd trial 13.35ml EDTA x (0.004M/1000ml) x (100.1g CaCO3/1mole CaCO3) x (1000mg CaCO3/1g CaCO3) x (1000L/25.5ml) = 209.6 ppm CaCO3 3rd trial 13.50ml EDTA x (0.004M/1000ml) x (100.1g CaCO3/1mole CaCO3) x (1000mg CaCO3/1g CaCO3) x (1000L/25ml) = 216.2 ppm CaCO3 Average ppm (216.2 + 209.6 + 214.6)/3 = 213.5ppm CONCLUSION: The concentration was concluded to be 213.5 ppm in the unknown which is right about in between Phoenix’ water hardness which is 164-291 ppm. REFERENCE: Department of Chemistry.(2012,February).Complexometric Determination of Water Hardness.Mesa Arizona City of Phoenix Official Website http://phoenix.gov/waterservices/quality/index.html