Carolina Investigations® for Use with AP® Chemistry: Evaluating the Extent of Buffering Capacity of Various Household Products Kit

Students evaluate a buffer solution's buffering capacity and compare the titration curves of a buffer solution and a weak acid. This comparative laboratory exercise can be taught using either a guided or an inquiry activity. In the guided activity, students measure the pH of a citric acid solution titrated with a strong base and plot the titration curve. Students repeat the procedure with a solution prepared from a commercial lemonade mix, which behaves as a buffer and whose primary ingredient is citric acid. Students compare the 2 titration curves, make observations, and address the differences in the curves.

The inquiry activity allows students to design a procedure to evaluate a commercial lemonade mix's buffering capacity. It also provides an opportunity for students to present their experimental design and results, reinforcing the practice of communicating findings. Detailed preparation and procedure notes guide the teacher through leading a successful inquiry activity, including a suggested rubric for assessing student performance.

Both activities include assessment questions that follow the AP® Chemistry Exam free-response question format. In the assessment, students predict how changes in acid concentration and the acid-to-conjugate base ratio affect a titration curve's shape. Students understand that changes in acid concentration and conjugate base increase a solution's buffering capacity, while changes in the acid-to-conjugate base ratio determine a solution's pH.

This kit provides the following AP® Chemistry experiences: design a procedure to collect data, analyze data, make predictions about chemical changes, perform a titration, use a pH meter and a buret, and plot a titration curve. The use of a commercial lemonade mix as a buffer helps students make the connection between chemistry and their everyday lives. Materials are sufficient for 30 students working in groups of 3. Digital teacher's manual, included FREE with kit purchase, is a 12-month eBook license to the Evaluating Lemonade as a Buffer teacher's manual. You can also access the digital student guide for this kit for free at Carolina Science Online®.

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