EDTA Titration of the Hardness of Water
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Experiment 6: EDTA Titration of the Hardness of Water Introduction: This experiment is meant to introduce you to creating your own procedure and following it in order to complete a specific experiment. Water and Tums will be titrated with EDTA and the calcium content will be calculated. Procedure: Calibrate a pH meter in order to test the pH of and ammonia buffer. Add 1M HCl to the buffer until the pH is about 10. In a 500mL volumetric flask make about 0.01M EDTA adding 8mL of the buffer. Then dissolve 0.5g CaCO3 in 100mL of 0.1M HCl. In an Erlenmeyer flask combine 3mL CaCO3 solution, 5mL buffer, and calmagite indicator. Titrate this with the EDTA until there is a blue endpoint. DO this until you have three good trials. Repeat this procedure using tap water instead of the CaCO3 solution. Then do a third set of titrations testing an antacid. In volumetric flask add 1.2925g of tablet and dilute to 100mL using 0.1M HCl. In an Erlenmeyer flask combine 3mL antacid solution, 5mL buffer and indicator. Titrate using EDTA and again there will be a blue endpoint. Do this until three good trials are obtained. Data: Masses EDTA: 1.8612g CaCO3: 0.5052g Standardization Trial 1 2 3 Average Volume EDTA used (mL) 15.0 14.21 13.27 14.16 Molarity of EDTA (M) 0.0101 0.0107 0.0114 0.0107 Determining the Hardness of Water Trial 1 2 3 Average Volume EDTA used (mL) 2.58 2.42 2.72 2.56 Ca2+ Concentration (M) 0.00104 0.001036 0.001164 0.001101 ppm in Water 44.25 41.52 46.65 44.14 Determining mass % of Ca2+ in Antacid Tablet Trial Volume EDTA used (mL) 1 15.35 2 14.66 3 14.06 Average 14.69 Manufacturer’s claim: 15.74% Ca2+ per tablet Ca2+ in Tablet (g) 0.2194 0.2095 0.2.010 0.1260 Mass % Ca2+ in Tablet 17.25 16.47 15.80 16.51 Calculations: Grams of EDTA needed πππππ πππ π πΈπ·ππ΄ ππππ ππππ ∗ ππππ ππππ ∗ = π ππππππ 1 πππ πΈπ·ππ΄ Molarity of EDTA π πΆππΆπ3 ∗ π πΆππΆπ3 ∗ 1 = π πΈπ·ππ΄ π πΈπ·ππ΄ Moles of CaCO3 1 πππ πΆππΆπ3 ππΆππΆπ3 ∗ = πππ πΆππΆπ3 100.087π Molarity of CaCO3 πππππ πΆππΆπ3 =π π Moles of EDTA ππ’π ππ ∗ π ππ πΈπ·ππ΄ = πππππ Ca2+ Concentration in Tap water 0.0505π πΆππΆπ3 ∗ 0.003ππΏπΆππΆπ3 1 ∗ = 0.0101π πΈπ·ππ΄ 0.01500ππΏπΈπ·ππ΄ Moles of CaCO3 Example 0.5052π ∗ 1 πππ πΆππΆπ3 = 0.005048πππ πΆππΆπ3 100.087π Molarity of CaCO3 Example 0.005048πππππ πΆππΆπ3 = 0.0505π 0.100πΏ Moles of EDTA Example 0.00258 ∗ 0.01π ππ πΈπ·ππ΄ = 0.000028πππππ Ca2+ Concentration in Tap water for Trial 1 Hardness of Water πππππ πππ π 1000ππ Μ ∗ πΆπ2+ π ∗ = πππ 1 πππ 1π 1 πππ πΆπ2+ 1 πππ ∗ = 0.001104π 1 πππ πΈπ·ππ΄ 0.025πΏ Hardness of Water example 40.078π 1000ππ 0.001101π ∗ ∗ = 44.13 πππ 1 πππ 1π Mass % Ca2+ expected in tablet Mass % Ca2+ expected in tablet example π πΈπ·ππ΄ ∗ π πΈπ·ππ΄ ∗ 1 πππ πΆπ2+ 1 πππ ∗ = πΆπ2+ ππππ 1 πππ πΈπ·ππ΄ π π€ππ‘ππ Grams of EDTA needed Example 292.14π πΈπ·ππ΄ 0.01π ∗ 0.500πΏ ∗ = 1.8616π ππππππ 1 πππ πΈπ·ππ΄ Molarity of EDTA for Trial 1 1πππ 1πππ πΆπ2+ 40.078π ππΆππΆπ3 ππ π‘ππ ∗ ∗ ∗ = π πΆπ2+ 100.0869π 1πππ πΆππΆπ3 1πππ 2+ π πΆπ = πππ π % π π‘πππππ‘ Tums Tablet Experiment π πΈπ·ππ΄ ∗ π πΈπ·ππ΄ ∗ Percentage 1 πππ πππππ πππ π 33.33 ππππ‘π ∗ ∗ =π 1 πππ 1 πππ π πππ’π‘πππ πππ π ππ πΆπ2+ πππππ’πππ‘ππ ∗ 100 = % πππ π ππ π‘πππππ‘ 0.00258πΏ ∗ 0.0107π ∗ 0.5ππΆππΆπ3 ∗ 1πππ 100.0869π ∗ 1πππ πΆπ2+ 1πππ πΆππΆπ3 ∗ 40.078π 1πππ 2+ = 0.20023π πΆπ2+ 0.20023π πΆπ = 15.74 % 1.2720π π‘πππππ‘ Tums Tablet Experiment Example 0.01535πΏ ∗ 0.0107π ∗ 1 πππ 40.078π 33.33 ππππ‘π ∗ ∗ = 0.2194π 1 πππ 1 πππ π πππ’π‘πππ Percentage for Trial 1 0.2194π ∗ 100 = 17.25% 1.2720π Conclusion: This lab had to objectives, to determine the Ca2+ concentration in tap water and the Ca2+ concentration in an antacid tablet and compare it to the manufacturer’s claims. After some calculations I found that since the manufacturer claimed there was 40% CaCO3 in each tablet there was 15.74% Ca2+ in each tablet. After the experiment our three trials gave a larger mass percent than expected according to the claims of the manufacturer. The percentages averaged at 16.51% which is a 4.89% error from the expected value. A source of error could have been from determining the end point because it would often go back to pink and not stay at the end color, which is blue. We may have added more titrant than needed thinking that it had yet to reach the end point but in reality it had. In the future maybe we should have recorded the volume of EDTA added when we first noticed a color change. Either way we were very close to the manufacturer’s claim and it is possible that the tablet could have had more calcium than expected. The other objective of this lab was to determine the hardness of tap water, amount of Ca2+, and we calculated there to be an average of 44.14ppm over our three trials.
