By Mikayla Messing
To examine the effectiveness of buffers by titrating two sets of five different solutions using HCl and NaOH and monitoring the pH change of the various solutions. The data collected shows that the buffer systems made with sodium acetate and acetic acid were effect when titrated with the strong acid and the strong base. Comparison of all the solutions shows that the concepts of buffers holds true for the results from the experimentation. Introduction
The main objective of this lab was to test the ability of buffered and unbuffered solutions to resist changes in pH with the addition of strong acids and strong acid. This will be accomplished by making two sets of five different solutions. They will be made using water, a salt solution (sodium chloride), and various concentrations of a buffer. Once the solutions are made, one set of the five will be used to observe the changes in pH made by adding hydrochloric acid (HCl) drop by drop. The second set of the five solutions will be used to observe the changes in pH made by adding sodium hydroxide (NaOH) drop by drop. It is predicted that the first two solutions with water and the salt solution will experience immediate drastic changes in their pH. This will happen because neither solution has conjugates in their systems. The other three solutions will resist a change in pH until its buffer capacity is reached. The solution with the highest concentration of the buffer will be the most effective at resisting pH changes. This is because buffers become more effective as their concentration increases. Therefore, the buffer system with the greatest amount of sodium acetate will be the most effective buffer.
Five different buffer solutions were made twice to make ten buffer solutions; one set was be used to observe the changes in pH caused by adding a strong acid (HCl) and the other set was used to observe the changes in pH caused by adding a strong base (NaOH). The five solutions made were distilled water, .10 M sodium chloride (NaCl), a solution of 1 gram of solid sodium acetate (CH3COONa) and 50 milliliters (mL) of acetic acid (CH3COOH), a solution of 5 grams of solid sodium acetate and 50 mL of acetic acid, and a solution of 10 grams of solid sodium acetate and 50 mL of acetic acid. The specific contents of the ten beakers are as follows: beakers 1 and 6 contained 50 mL of distilled water. Beakers 2 and 7 contained 50 mL of a NaCl solution. Beakers 3 and 8 contained 1 gram of solid sodium acetate and 50 mL of acetic acid. Beakers 4 and 9 contained 5 grams of solid sodium acetate and 50 mL of acetic acid. Beakers 5 and 10 contained 10 grams of solid sodium acetate and 50 mL of acetic acid. A special probe was used to monitor the pH of one set of each solution as HCl was added drop by drop. The results were recorded in a table found later on in the report. The probe was also used to monitor the second set of solutions as NaOH was added drop by drop. For more detailed instructions on the instructions for mixing the solutions and other experimental details, refer to Chemistry 110 lab manual by Kautz, Kinnan, and McLaughlin.
The series of experiments were conducted and the pH was recorded with every drop of the strong acid or strong base. It was revealed through the experimentation that the distilled water and sodium chloride were not effective buffers. The solutions of sodium acetate and acetic acid were good buffers; the effectiveness of the solution increased as the concentration of sodium acetate increased. The solution with 10 grams of sodium acetate was the most effective of the buffers, followed by the solution made with 5 grams of sodium acetate and the solution made with 1 gram. Effectiveness of these solutions were shown through the addition of both the HCl and the NaOH. Table 1.1 below shows the change in pH when beakers one through five were titrated with 1.0 M hydrochloric acid....
References: Kautz, J., D. Kinnan, and C. McLaughlin. Chemistry 110 Laboratory Manual Hayden-McNeil,
Tro, Nivaldo. Chemistry: A Molecular Approach. Upper Saddle River, NJ: Pearson Education,
Inc., 2008. Print.
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