TRIGGER/PROMPT pH TITRATION PROCEDURE

1. Prepare the solution to be titrated as directed by your teacher.

2. Place the beaker on a magnetic stirrer and add a stirring bar. If no magnetic stirrer is available, you need to stir with a stirring rod during the titration.

3. Prepare the pH system for data collection.

• Plug the pH amplifier into the adapter cable in Channel 1 of the CBL. The pH electrode is already connected to the pH amplifier.
• Connect the CBL System to the TI-8X calculator with the link cable using the port on the bottom edge of each unit. Firmly press in the cable ends.

4. Use a utility clamp to suspend a pH electrode on a ring stand. Position the pH electrode in the solution to be titrated and adjust its position so that it is not struck by the stirring bar.

5. Obtain a 50-mL buret and rinse the buret with a few mL of the titrant solution. Dispose of the rinse solution as directed by your teacher. Use a utility clamp to attach the buret to the ring stand Fill the buret a little above the 0.00-mL level of the buret with basic solution. Drain a small amount of the solution so it fills the buret tip and leaves the solution at the 0.00-mL level of the buret. Record the precise concentration of the titrant solution in your data table.

PREPARING THE CBL SYSTEM

6. 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.

7. 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 directed otherwise by your teacher.

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

• Select COLLECT DATA from the MAIN MENU.
• Select TRIGGER/PROMPT from the DATA COLLECTION menu.

9. Press ENTER after the pH system has warmed up 30 seconds. Before adding titrant, monitor the pH value on the CBL screen. Once the pH has stabilized, press TRIGGER on the CBL and enter "0" (the buret volume, in mL) in the TI-8X calculator. You have now saved the first data pair for this experiment.

10. You are now ready to begin the titration. This process goes faster if one person manipulates and reads the buret while another person operates the calculator and enters volumes.

• Select MORE DATA to collect another data pair. Add the next increment of titrant (enough to raise the pH about 0.15 units). When the pH stabilizes, press and enter the current buret reading (to the nearest 0.01 mL). You have now saved the second data pair for the experiment.
• Select MORE DATA. Continue adding titrant solution in increments that raise the pH by about 0.15 units and enter the buret reading after each increment. When a pH value of approximately 3.5 is reached, change to a one-drop increment. Enter a new buret reading after each increment. Note: It is important that all increment volumes in this part of the titration be equal; that is, one-drop increments.
• After a pH value of approximately 10 is reached, again add larger increments that raise the pH by about 0.15 pH units, and enter the buret level after each increment.
• Continue adding titrant solution until the pH value remains constant.

11. Select STOP AND GRAPH.

12. ENTER, QUIT to return to the home screen.

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