Procedure

1. Assemble your equipment as directed by your professor.
2. Rinse and fill the plastic reagent reservoir with NaOH.  Remove any air bubbles from the tip of the reservoir and adjust the flow rate of the two valves of the reagent reservoir by completely opening the bottom two-way valve and slowly opening the top valve until a rate of one drop per second is achieved.
3. Launch Logger Pro on your computer. From the Probes & Sensors folder, select the Drop Counter folder, then open the Drop Counter-pH file.
4. To calibrate drops so that the volume of the titrant is recorded in units of milliliters, place a 10 mL graduated cylinder below the slot of the drop counter.  Start the automatic calibration in Logger Pro and open the bottom valve to begin releasing drops.  Continue releasing drops until there are between 9 and 10 mL of NaOH in the graduated cylinder.  Type the precise volume of the NaOH in the graduated cylinder in the Volume (mL) box of the calibrate drops dialog box.
5. Calibrate the pH probe with the pH 4 and pH 10 buffer solutions. Adjust the precision of the pH to record to the nearest + 0.01 pH units. Attach a Vernier microstirrer to the tip of the pH probe in a manner that allows it to spin freely (see the Drop Counter sensor booklet for photo or click here).
6. Using a clean pipet, dispense 50.00 mL of the first acid into a 100-mL beaker. Rinse the pH probe and place it into the beaker. Once again, make sure the microstirrer spins freely.
7. Before adding any NaOH, click on "Collect".  Data collection will begin once the first drop passes through the drop counter's slot.
8. Continue adding drop-by-drop until until the graph levels off around a pH of 12-13. 
9. Stop the Data Collection process. Save your data using the following convention: Lastname1 Lastname2 Lab 10.
10. Repeat steps 6 through 9 with the other two acids.
11. Waft fumes of each acid toward your nose. Record any familiar odors. This may aid in your identification of the acids.

Data Analysis and Questions

1. Copy and paste your data into an Excel spreadsheet. In your spreadsheet, create a new column labeled first derivative. Your instructor will demonstrate how to calculate the first derivative of your pH and volume data. Then graph your data on the spreadsheet. 
2. Classify each of the unknown acids as
   a)  weak or strong, and
   b)  monoprotic or polyprotic.
3. For each monoprotic acid, use the first derivative to determine the volume of base required to reach the equivalence point. 
4. Clearly label each of the graphs. Due to the large amount of data, do not print out copies of your graphs. 
5. Find the initial molarity of each of the monoprotic acids from the volume of base required to reach the equivalence point. (See Section 4.10 in Ebbing & Gammon. Also see problems 17.115-17.116)
6. For the acid you identified in #5 as the weak acid, calculate the K_a from its initial pH and molarity. (See Chapter 17.)
7. The halfway point is defined as one-half of the volume required to reach the equivalence point. In the titration of a weak acid with a strong base, it can be shown that pH = pK_a at the halfway point. Find the pH at the halfway point. Then use it to determine the pK_a. Then use the pK_a to determine the K_a for your weak acid. 
8. Compare the two K_a values that you obtained above with the accepted K_a value for your weak acid. (Which weak acid do you think you have? Hint: Waft the fumes toward your nose. Then find the K_a for the weak acid in your text.) Calculate the percent error of each result.

Laboratory Report
For this experiment, follow the Group Laboratory Report Guidelines located at http://webs.anokaramsey.edu/chemistry/chem1061/labs/Reports/GroupReports.htm. You have the option of submitting an individual report. If you do so, please signify on your report that it is an individual report. Guidelines for Individual Laboratory Reports may be found at http://webs.anokaramsey.edu/chemistry/chem1061/labs/Reports/IndReports.htm. Use the Print Preview feature to help conserve paper in the laboratory. 

Please show a set of calculations that support your answers. You may use Microsoft Equation 3.0 objects placed into a Microsoft Word document or formulas in Excel to show your calculations. Submit your Excel spreadsheet as an email attachment to your professor (laura.miller@anokaramsey.edu or lance.lund@anokaramsey.edu) using a filename convention of Lastname1 Lastname2 Lab10, and a subject line of "Chem 1062: Titration Lab"). Be sure to include all answers to the questions in the Data Analysis and Questions sections.

Lab written by Lance S. Lund, Anoka-Ramsey Community College.