pH Titration REBECCA FORLOINE LAB PARTNER: TERRENCE CONNORS FEBRUARY 24, 2015 Having read the Georgia Institute of Technology Academic Honor code, I understand and accept my responsibility as a member of the Georgia Tech Community to uphold the Academic Honor Code at all times. In addition, I understand my options for reporting honor violations as detailed in the code.
Introduction In an acid-base titration, the concentration of a basic or acidic solution can be determined by titrating it with a volume of a standard opposite solution of known concentration required to neutralize it. The purpose is to find the equivalence point, the point at which the moles of acid equal the moles of base. In this experiment, the concentration of phosphoric acid in commercial cola was determined using an acid-base titration. Weak acids are only partially ionized in aqueous solution, so the phosphoric acid in water equation looks like the following dynamic equilibrium equation: − ¿ ( aq ) − ¿ ( aq ) + O H ¿ H 3 PO 4 ( aq ) + H 2 O ( l ) ↔ H 2 PO 4 ¿ The neutralization reaction for the weal phosphoric acid titrated by a strong base, NaOH is given by: − ¿ ( aq ) + H 2 O ( aq ) − ¿ ( l ) ↔ H 2 PO 4 ¿ H 3 PO 4 ( aq ) + O H ¿ Since this is a triprotic acid, the acid continues to react with the hydroxide until all protons have been stripped from the acid. A base is added, the concentration of HA progressively decreases while the concentration of A- progressively increases. At the equivalence point, the number of moles of hydroxide is equal to the number of moles of phosphoric acid that have been neutralized which is all of the initial amount. At the second equivalence point, the same holds true for hydroxide and phosphorous acid. Our hypothesis during this experiment was that at the first halfway point in the titration of phosphoric acid with sodium hydroxide the pH would be equal to the pKa1 of phosphoric acid. The same would be true for the second halfway point and the pKa2. In the lab manual the Ka1 is given as 7.5E-3 and the Ka2 is given as 6.2E-8.
You've reached the end of your free preview.
Want to read all 7 pages?
- Fall '12
- pH, Sodium hydroxide, Phosphoric acid