UMass Amherst CHEM 112 - Chem 112 Lab Report 5 (1) (3 pages)

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Chem 112 Lab Report 5 (1)



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Chem 112 Lab Report 5 (1)

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Pages:
3
School:
University of Massachusetts Amherst
Course:
Chem 112 - Gen Chem-Sci

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Chem 112 PH Titration Curves Idealized Purpose The purpose of this lab is to see the results of titration with two acids and see what a titration curve looks like and how to interrupt it and to determine dissociation constants for phosphoric and citric acid Calculations Citric acid equivalence point V1 19 33mL 1 3 V3 V2 38 63mL 2 3 V3 V3 58mL from graph V midpoint 1 9 67mL V1 V midpoint 2 28 98mL V1 V2 V midpoint 3 48 32mL V2 V3 At midpoint pH pKa Then pKa log H so H 10 pKa this is how to find Ka pH1 pKa1 2 9 H 00126 pH2 pKa2 4 5 H 000032 pH3 pKa3 6 4 H 00000039 Ka1 1 26E 3 Ka2 3 2E 5 Ka3 3 9E 7 Phosphoric acid equivalence point V1 18 1mL from graph V2 36mL from graph V3 54 3mL 3 V1 V midpoint 1 9 05 V1 V midpoint 2 27 05 V1 V2 V midpoint 3 45 15 V2 V3 At midpoint pH pKa Then pKa log H so H 10 pKa this is how to find Ka pH1 pKa1 2 9 H 00126 pH2 pKa2 6 8 H 00000016 pH3 pKa3 11 1 H 0000000000079 Ka1 1 26E 3 Ka2 1 6E 7 Ka3 7 9E 12 Discussion In the experiments the third equivalence point on the graph for Phosphoric Acid is not visable because it is so basic at this point similar to how the first 2 equivalence points on the graph for Citric Acid are not visible because it is so acidic By looking at the graphs of both acids neither shows all three of the acids equivalence points so in order to find them we had to calculate what they would approximately equal with what we know about the other equivalence points This can account for if there were some differences among group members in the Ka values since they were mostly done by interpretation of the graph and then calculations The pKa values given by the procedure for both acids differ from the ones we obtained in our experiment this could be caused by an experimental error or human error while none of the values match up perfectly the powers seen in the results for citric acid and the procedure match up well Results The purpose of this experiment was to determine the dissociation constants for phosphoric and citric acid



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