1. Prepare 250 ml of an approximately 0.05 M oxalic acid solution by dissolving 1.125 g oxalic acid in enough water to make 250 ml of solution.
2. Add several drops of phenolphthalein indicator solution to a clean 125 ml beaker.
3. Carefully transfer 40.0 ml of the oxalic acid solution to the Erlenmeyer flask.
4. Calibrate your pH meter with pH 7 and pH 4 buffers.
5. After wiping all fluid from the electrode, place it into the beaker containing the acetic acid.
6. Slowly titrate the oxalic acid with the 0.1 N KOH solution previously prepared, using proper titration technique.
7. Take pH measurement with the addition of every 0.2 mL added base.
8. Record pH values in your notebook.
9. Make note of any color changes in the indicator.
10. Discontinue addition of base when the pH reaches 12, or when the pH stops increasing after pH 11.
11. [At home] Plot the pH v. the volume of added base, and calculate the pKa of acetic acid.
12. repeat steps 1 - 12 for second (unknown, polyprotic acid), provided by the instructor.
13. Carefully clean up your place, cleaning and drying all glassware.
© 2005 by Lawrence T. Sein. All rights reserved.
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