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. Check to make sure that the drop counter is aligned properly, that the beam lens is free of debris (or dried NaOH), and that drops are being registered by Logger Pro.
5. 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.
6. 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). Note that pushing the microstirrer too far onto the pH probe may result in the bulb on the probe being broken. 
7. 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.
8. Before adding any NaOH, click on "Collect".  Data collection will begin once the first drop passes through the drop counter's slot.
9. Continue adding drop-by-drop until the graph levels off around a pH of 12-13. 
10. Stop the Data Collection process. Save your data using the following convention: Lastname1 Lastname2 Lab 10.
11. Repeat steps 7 through 10 with the other two acids.
12. 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 (to be incorporated into Results and Discussion)

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 4.8 in Tro. Also see problems 16.119-16.120)
6. For the acid you identified in #5 as the weak acid, calculate the K_a from its initial pH and molarity. (See Chapter 15.)
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 Laboratory Report guidelines located at http://webs.anokaramsey.edu/chemistry/chem1062. Follow your instructor's directions for submitting this lab report. (If you submit electronically, be sure to use a filename convention of Lastname1 Lastname2 Titration, and a subject line of "Chem 1062: Titration Lab").  

For this lab report, you will need to include a title, procedure, results (include the graphs—the data tables can be submitted as an appendix), discussion, and references. You may use the above questions to guide your discussion, but the discussion should be more than just answering the questions and should flow logically as you discuss the lab and the results. You will need to show sample calculations when reporting the results/discussion for some of the questions. You may present these in the report itself or in an appendix, and they can be handwritten or typed using an equation editor in Word. Alternatively, you may work the results into an embedded Excel spreadsheet that can be opened by your professor to show the formulas used for calculations if you choose to submit the report electronically. 

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