f. Discard the drained NaOH solution in the 250 mL beaker as directed.
Advanced Chemistry with Vernier 7 - 5 Acid-Base Titration 5. Calibrate the Drop Counter so a precise volume of titrant is recorded in units of milliliters. a. Choose Calibrate from the Sensors menu and select Drop Counter. If you have previously calibrated the drop size of your reagent reservoir and want to continue with the same drop size, select Equation. Enter the value for the Drops/mL and select Apply. Select OK and proceed directly to Step 6. If you want to perform a new calibration, select Start and continue with this step. b. Place a 10 mL graduated cylinder directly below the slot on the Drop Counter, lining it up with the tip of the reagent reservoir. c. Open the bottom valve on the reagent reservoir. Keep the top valve closed. d. Slowly open the top valve of the reagent reservoir so that drops are released at a slow rate (~1 drop every two seconds). You should see the drops being counted on the screen. e. When the volume of NaOH solution in the graduated cylinder is between 9 and 10 mL, close the bottom valve of the reagent reservoir. f. Enter the volume of NaOH and select OK. g. Discard the NaOH solution in the graduated cylinder as indicated by your instructor and set the graduated cylinder aside. 6. Assemble the apparatus. a. Place the magnetic stirrer on the base of the ring stand. b. Insert the pH Sensor through the large hole in the Drop Counter. c. Attach the Microstirrer to the bottom of the pH Sensor. Rotate the paddle wheel of the Microstirrer, and make sure that it does not touch the bulb of the pH Sensor. d. Adjust the positions of the Drop Counter and reagent reservoir so they are both lined up near the center of the magnetic stirrer. e. Lift up the pH Sensor, and slide the 100 mL beaker containing the HCl solution onto the magnetic stirrer. Lower the pH Sensor into the beaker. f. Adjust the position of the Drop Counter so that the Microstirrer on the pH Sensor is just touching the bottom of the beaker. g. Adjust the reagent reservoir so its tip is just above the Drop Counter slot. h. Turn on the magnetic stirrer so that the Microstirrer is stirring at a fast rate. 7. You are now ready to conduct the titration. a. Start data collection. No data will be collected until the first drop goes through the Drop Counter slot. b. Fully open the bottom valve. The top valve should still be adjusted so drops are released at a rate of about 1 drop every 2 seconds. When the first drop passes through the Drop Counter slot, check the graph to see that the first data pair was recorded. c. Continue watching your graph to see when a large increase in pH takes place—this will be the equivalence point of the reaction. When this jump in pH occurs, let the titration proceed for several more milliliters of titrant. d. Stop data collection, then turn the bottom valve of the reagent reservoir to a closed (horizontal) position.
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- Fall '19
- pH, Sodium hydroxide, pH sensor