Experiment 20: pH Titration: Phosphoric Acid in Cola DrinksJoy ThompsonPartner: Lauren TrasterTA: Michael EvansFebruary 26, 2014Chemistry 1212 A-09Honor Pledge“I did not share any part of this lab report after it was finished.”
II. IntroductionAcid-Base titrations are most commonly used to find the amount of a known acidic or basic substance through acid base reactions. The analyte is the solution with an unknown molarity, and the reagent is the solution with a known molarity that will react with the analyte. The analyte is prepared by dissolving the substance being studied into asolution which is usually placed in a flask for titration with a small amount of indicator. The reagent is usually placed in a burette and slowly added to the analyte. The amount ofreagent used is recorded when the indicator causes a change in color. You can also perform an acid base titration by using a Lapquest or other software to track the changes in pH as you add a reagent to an analyte. The point at which the solution changes color or where the pH of the solution changes most rapidly(as noticeable on a graph) is the equivalence point where the reagent has neutralized the analyte and the number of moles of acid and base are equivalent. For our experiment, we titrated degassed coca cola with NaOH. Since thephosphoric acid in coke is a polyprotic acid, we are using our titration to find the multipleKa values. For each value of Ka, H3PO4is deprotonated once. The Kavalues found fromthe titration can be expressed in the chemical reactions:H3PO4+H2O⇌H3O++H2PO4-H2PO4-+H2O⇌H3O++HPO42-HPO42-+H2O⇌H3O++PO43-The standardization of this reaction is KHC8H4O4(aq) + NaOH (aq) →NaKC8H4O4(aq) + H2OWe can assume that the first Kavalue will be the largest followed by second andthen the last. This can be validated by Bottomley and Bottomley’s Chemical Principles I& II, which states the literature values to be Ka1as 7.5X10-3, Ka2as 6.2X10-8, and Ka3as2.2X10-13. In this experiment we can also assume that at the equivalence points in Part Bwe will see drastic increase in the graph of the pH vs titrant and that we will see a similaryet less drastic increase in the graph at the second equivalence point.In this experiment we will be able to successfully standardize the sodiumhydroxide solution with KHP to obtain the concentration of NaOH at this point. We alsowere able to determine both equivalence points in the titration of cola and could thendetermine both values of Ka. The concepts of titrating and using the date to find hallwaypoints were made evident in this lab. Titrating is a technique used in multiple industries.Even the most basic of titrating techniques are used commonly in real life scenarios. Oneexample is that environmental scientists use titration in order to analyze precipitation andits response to pollution. Titration is used to determine the level of contamination ofwater or snow.
- Spring '11
- pH, Equivalence point, Sodium hydroxide, KHP