Small Scale Dropwise Titrations with the CBL

SMALL SCALE pH TITRATION PROCEDURE

1. Prepare the solution to be titrated in a 50 ml beaker or one well of a well plate.

2. Turn on the CBL unit and the TI-8X calculator. Press PRGM and select CHEMBIO. Press ENTER, then press ENTER again to go to the MAIN MENU.

3. Set up the calculator and CBL for pH measurement.

Select SET UP PROBES from the MAIN MENU.
Enter "1" as the number of probes.
Select PH from the SELECT PROBE menu.
Enter "1" as the channel number.
USE the STORED CALIBRATION, unless otherwise directed by your teacher.

4. Set up the calculator and CBL for data collection.

Select COLLECT DATA from the CHEM MAIN MENU.
Select TRIGGER from the DATA COLLECTION menu.
Press ENTER after the pH system has warmed up 30 seconds.

5. Add one drop of indicator solution to the well containing the solution to be titrated.

6. Draw the solution out of the well and into a clean beral pipette. Replace the solution into the same well. This beral pipette will serve as a mixing tool in the titration. When you are asked to mix the reaction, follow this procedure.

7. Before adding the titrant, put the pH electrode into the solution to be titrated and monitor the pH value on the CBL screen. Once the pH has stabilized, press TRIGGER on the CBL. You have now saved the first data point for this experiment.

8. You are now ready to begin the titration.

9. Add the titrant drop-wise to the well, taking note to mix the reaction after each drop and recording the pH as in the procedure that follows.

Select MORE DATA on the calculator after each drop to collect another data point
Continue adding base solution until the pH value remains constant.

10. Select STOP when done titrating, and QUIT to view data.

11. Dispose of the beaker/well contents as directed by your teacher. Rinse the pH electrode and return it to the storage solution.

Graphing

Your pH values are stored in List L1. In order to create a titration curve you need to manually enter drop number values in list L2, or use the DROP program.

To set up the graph: