Report

A separate report is expected from each student. You may discuss your ideas with other students, but you should state your answers in your own words.

Type your report. If you write it out by hand, please write clearly.

Your report will run to several pages. Staple your pages together. Your instructors are not responsible for loose or lost pages.

Due: By midnite, the day after your normal lab day, e.g., Monday lab students must turn their reports in sometime Tuesday night. Place your lab report in Alan's box outside Rm. 303 (department office). Do not turn in your notebook.

Heading

Write your first and last name, your box number, your lab day, and the title of the experiment at the top of your report.

Data table and experimental parameters

Construct a table with the following column headings (units are in parentheses, explanatory comments are in italics; do not put my comments in your table):

• Sample - number 1-8
• Vol Acidic BCG (mL) - amount used
• Vol Basic BCG (mL) - amount used
• Abs - measured value
• pH - measured value
• [BCG^-2]/[HBCG^-] - value calculated from absorbance
• log₁₀[BCG^-2]/[HBCG^-]
• [AcO^-]/[AcOH] - stoichiometric ratio
• log₁₀[AcO^-]/[AcOH]

Enter your data in the table using one row for each sample.

After your table, list your partner's name(s). If you used a special reduced volume spectrophotometer cell, say so.

Data Analyses

The data analysis for this experiment is quite simple: you just need to convert your data into estimates of the pKa's of BCG and acetic acid. However, you must arrive at, and present, these estimates in a particular way.

1. Perform two separate analyses, one for each acid.

2. Base each analysis on the Henderson-Hasselbach equation. This equation provides a mathematical relationship between pK_a and two other quantities, both of which you have measured. Therefore, your analysis should work from these measurements towards pK_a.

3. Don't tell me about the H-H equation, how you plan to use it, or show me your calculations.

4. Do show me the results of analysis in the form of a graph. The graph should be based on the variables identified by the H-H equation as important. The graph should show 1) your measurements (plot these as separate points, do not connect the points), and 2) a smooth line or curve that shows a least-squares fit of the H-H equation to your measurements (use a curve fitting program or a programmable calculator to do the curve fitting). A graph containing data points and least-squares line should look something like this (of course, you must also label your axes and mark off grid points on each axis):

5. Do show me the results of your least-squares fit in the form of an equation and a value for pK_a.

6. Do compare your pK_a to a published experimental value (and provide a citation for this publication).

Molecular Modeling

The instructions for the molecular modeling portion of this experiment contain questions that need to be answered using molecular models and will be distributed in lab. If you like, you can download a copy of the instructions here. Your modeling data, and answers to any questions about these models, should be stapled at the rear of your report.