Water Hardness Titration

July 28, 2018 General Studies

Procedure:

1. Gather the test tube holder, small stopcock, 10-mL syringe (titrator), and 2 thick textbooks and the LabPaq box or 5-6 thick textbooks. 2. Remove the plunger from the titrator and place it back in your LabPaq box. 3. Attach the stopcock to the tip of the titrator by placing the larger, clear, plastic end of the stopcock into the tip of the titrator and then twisting the stopcock into place. The stopcock should fit tightly into the titrator, so that the liquid will not leak. 4. Stack the textbooks on top of one another or stack two textbooks on top of the LabPaq box. 5. Clamp the test tube holder around the middle of the titrator and slide the long end under the top two books in the stack. Place a sheet of white paper next to the bottom of the stack and set the 100-mL beaker on the sheet of white paper.

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The end of the stopcock should be located near the top of the beaker, approximately 1 cm above to 1 cm below the top of the beaker. 6. Use the pipette to fill the titrator with 7—9 mL of distilled water. 7. Using both hands, one on the titrator and one on the stopcock, practice releasing water from the titrator into the beaker. The goal is to be comfortable releasing only one drop at a time from the titrator. 8. When you are comfortable using the titrator pour the water in the beaker down the drain, remove the titrator from the test tube clamp, and remove the stopcock from the titrator. Thoroughly dry each of these three items with paper towels.

9. When all items are completely dry, reassemble the titration setup. 10. Put on your safety gloves and goggles.
11. With the stopcock in the closed position, fill the titrator with 9 to 10 mL of the EDTA solution. 12. Move the beaker away from the titrator and place a crumpled paper towel directly below the titrator. 13. Using the stopcock, allow a few drops of the EDTA solution to flow through the titrator into the paper towel. This will fill the tip of the titrator with EDTA solution and remove any air bubbles from the titrator. 14. Place the paper towel with the EDTA drops into the trash and re-position the clean, dry 100- mL beaker back in the titration setup, under the titrator. 15. Use the graduated cylinder to measure exactly 10 mL of tap water from your sink. 16. Pour the 10 mL of tap water into the completely dry 100-mL beaker. 17. Add 5 drops of pH 10 buffer solution to the 10 mL of tap water in the beaker.

Carefully swirl the mixture in the beaker to ensure that the buffer is incorporated into the water. 18. Dip approximately 10 mm of a toothpick into the distilled water. Then, while toothpick is still damp, dip the toothpick into the EBT indicator powder. 19. Dip the EBT-covered toothpick end into the water in the beaker and carefully stir, to transfer all of the EBT from the toothpick into the water. 20. Carefully swirl the beaker for 30–60 seconds to fully dissolve the EBT into the water solution. 21. Read the volume of EDTA in the titrator and record in Data Table 1 under “Initial EDTA Volume (mL)”, next to Trial 1. 22. Open the stopcock and add 1 drop of EDTA to the purple-pink water sample in the beaker. After the drop is added, gently swirl the beaker and observe the color for 5 seconds. 23. Continue adding EDTA solution, one drop at a time, to the beaker, swirling and observing after each drop, until the color changes to a pale blue-gray color for at least 5 seconds. 24. Record the volume of the EDTA solution remaining in the titrator and record in Data Table 1 under “Final EDTA Volume (mL)”, next to Trial 1.

25. Determine the total volume of EDTA used by subtracting the final EDTA volume from the initial EDTA volume and record the volume in Data Table 1. 26. Leave the titrator assembly intact. You will need it for future titrations in this experiment. 27. Pour the contents of the beaker down the drain and flush the drain with water. Thoroughly wash the beaker with soap and water to remove all of the EDTA solution from the beaker. When the beaker is clean, rinse the beaker with distilled water and then thoroughly dry. 28. Place the clean and thoroughly dry beaker back in the titration set-up, under the titrator. 29. If necessary, add more EDTA solution to the titrator.

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