Laboratory Report for Experiment 21

Laboratory Report for Experiment 21 - uncertainty very much...

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Laboratory Report for Experiment #21: Titration of a Polyprotic Acid Kevin Ho Chem106, Section 10, Elsa 11/09/11 Summary: In this lab, I titrated an unknown polyprotic acid with a base to generate a pH titration curve using Excel. I then calculated the concentration and pk a values of the unknown acid by using the titration curve. Results: The concentration of the unknown acid is 0.8m. Ka’s for the unknown acid is 8.2*10 -2 and 2.0*10 -3 . Discussion: These values are fairly trustworthy. Because an excel program was used for all the calculations, they will be right according to the input values. I estimate that the uncertainty is less than 1%. The only uncertainty comes from the burette readings which is very slim and the calibration of the pH meter. I believe that my performance in this lab was very good; I performed to the best of my ability allowing myself extra time to take accurate readings. I believe I did not contribute to the
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Unformatted text preview: uncertainty very much by my performance. The only error I can account for is adding too much base during the first titration interval. I should have started by adding the base drop wise to the acid. I would advise someone who was doing this lab by telling them to stop adding base once the pH is 0.1 away from the desired level. 1. No base is present, acid concentration is dominant. pH is below 7. 2. Acid concentration is dominant over base concentration. pH is below 7. 3. Acid concentration is dominant over base concentration. pH is below 7. 4. Acid concentration is dominant over base concentration. pH is below 7 5. The acid and base concentrations are equal. Acid is deprotonated and is now HA. 6. Acid concentration is dominant over base concentration. pH is below 7....
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