Unit 6 Acid-Base Titration Lab
Exercise 6: Acid-Base Titrations
Nick Redmond
Partner: Stephan Villavicencio
Thurs. Section
Lab date: March 19, 1998
Report date: April 6, 1998
Abstract:
The equilibrium between acids and bases during a titration can be used to determine several characteristics of the acid or the base. Sodium hydroxide was standardized to 0.1035 M in three acid-base titrations of potassium hydrogen phthalate (KHP). This standardized NaOH solution was then used in a series of other titrations with acids in order to gain information about those acids. The first acid tested was hydrochloric acid. This titration showed that the equivalence point occurred at a pH of 7.0. The second acid tested was the polyprotic phosphoric acid. This titration resulted in two equivalence points, one at pH 5.01 and the second around pH 9.25. The pKa1 of this acid was 2.25 and pKa2 was 6.90, compared with the known values of 2.16 and 7.21, respectively. Three titrations with the unknown acid “O” showed that the molecular weight of the acid was 76.09 g/mol. This is approximately one-half the known molecular …show more content…
Looking more closely at the data, the amount of titrant added at this point was determined to be 31.43 ml. This means 3.25 x 10-3 moles of NaOH were needed to react with 3.0 x 10-3 moles of HCl. Because HCl is a strong acid and NaOH is a strong base, the Ka is very high. Essentially all the protons in equilibrium come from the acid, and not from water. This means before the equivalence point, pH is determined almost exclusively by the strong acid, and after the equivalence point it is determined by the strong base. At the equivalence point, the two cancel each other out, and the pH is a neutral 7.0. There is no use trying to find a half-equivalence point to find the pKa of the acid because the acid’s Ka is too large. The experimental data supports these qualities of a strong
Nick Redmond
Partner: Stephan Villavicencio
Thurs. Section
Lab date: March 19, 1998
Report date: April 6, 1998
Abstract:
The equilibrium between acids and bases during a titration can be used to determine several characteristics of the acid or the base. Sodium hydroxide was standardized to 0.1035 M in three acid-base titrations of potassium hydrogen phthalate (KHP). This standardized NaOH solution was then used in a series of other titrations with acids in order to gain information about those acids. The first acid tested was hydrochloric acid. This titration showed that the equivalence point occurred at a pH of 7.0. The second acid tested was the polyprotic phosphoric acid. This titration resulted in two equivalence points, one at pH 5.01 and the second around pH 9.25. The pKa1 of this acid was 2.25 and pKa2 was 6.90, compared with the known values of 2.16 and 7.21, respectively. Three titrations with the unknown acid “O” showed that the molecular weight of the acid was 76.09 g/mol. This is approximately one-half the known molecular …show more content…
Looking more closely at the data, the amount of titrant added at this point was determined to be 31.43 ml. This means 3.25 x 10-3 moles of NaOH were needed to react with 3.0 x 10-3 moles of HCl. Because HCl is a strong acid and NaOH is a strong base, the Ka is very high. Essentially all the protons in equilibrium come from the acid, and not from water. This means before the equivalence point, pH is determined almost exclusively by the strong acid, and after the equivalence point it is determined by the strong base. At the equivalence point, the two cancel each other out, and the pH is a neutral 7.0. There is no use trying to find a half-equivalence point to find the pKa of the acid because the acid’s Ka is too large. The experimental data supports these qualities of a strong