Page 2 Procedure Edta Titrimetric Method Total Hardness May Be Determined By Titration Against A Standard Solution Of E 1 (155.42 KiB) Viewed 19 times
Page 2 PROCEDURE: EDTA Titrimetric Method Total Hardness may be determined by titration against a standard solution of ethylenediaminetetraacetic acid (EDTA) using a mild chelating agent, such as Eriochrome Black T (EBT), as an indicator. 1. Place a small sample (exactly 25 mL) of the water to be tested into a 250-mL beaker and dilute to about 50 mL with distilled water. 2. Add 2 mL of 'hardness buffer' solution. This solution raises the pH to about 10. 3. Add a small amount of the EBT indicator. 4. If hardness is present, the solution will turn wine-red. If no hardness is present, the solution will turn gray-blue. 5. Assuming the solution turns wine-red, titrate with EDTA until the color just changes to gray-blue. Record the mL of EDTA added as 'A'. This titration must be done carefully, but fairly rapidly (5 minutes or less from the addition of the buffer to the completion of the titration). Extending the time period will cause erroneous results because some of the divalent cations will begin to precipitate as a result of the elevated pH. CALCULATIONS AND CONCLUSION: The calculation required for this lab is shown below: Total Hardness: TH= (A x B x 1000) / mL sample Where, TH= total hardness, mg/L as CaCO3 A = EDTA titrant required to reach the color-change endpoint, mL B = CaCO3 equivalence of the EDTA titrant (usually 1.0), mg/mL A. To the engineer, what is the most challenging problem associated with hardness? B. In areas where limestone is abundant, would you consider the water to be hard or soft? Why? Hard Water Sample Tap Water Sample mg CaCO3 equivalent to 1.00 mL EDTA titrant Be sure to address the following questions in your report: RAW DATA: Initial Burette Reading (in mL) Final Burette Reading (in mL) Total EDTA of 2 ZOOM + ak
Inial Burette Reading (mL) Final Burette Reading (mL) Total EDTA Hard Water Sample Tap Water Sample 17.9 24.8 24.8 31.8 6.9 7
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