Question

Procedure 1. Arrange the burette and other equipment as shown in Figure 1. Use a 250-ml Erlenmeyer flask for the titration 2. Fill the burette with NaOH solution using a funnel. (Wear goggles and gloves!) Record the concentration (molarity) of the base in the Data Table on the Worksheet. 3. Measure out 100 mL of flat Mountain Dew in a graduated cylinder and transfer it to the 250-ml Erlenmeyer flask. (If you will be using a magnetic stirrer, place a stir bar in the flask as well.) 4. Add 2-3 drops of the phenolphthalein indicator solution to the soft drink. Since the indicator is colorless in acidic solution, the color of the liquid should not change. 5. Clear any air bubbles from the delivery tip by draining and discarding some NaOH solution. 6. Read the level of the NaOH solution in the burette at the meniscus, and record the starting volume in the Data Table 7. Place the mouth of the Erlenmeyer flask under the delivery tip of the burette, with the tip just inside the mouth. (If you are using a magnetic stirrer, the flask sits atop the stirring motor.) 8. Swirl the flask by hand for start the stirrer) as you drain NaOH solution from the burette. The total volume needed will be somewhere between 20 and 30 mL. When you begin to see a few 160 Estimating the Acid Content of a Soft Drink streaks of a different color appear in the flask, stop adding the base. Knock the drop of liquid on the delivery tip into the flask. 9. When the neutralization of the citric acid is complete, the first extra droplet of NaOH will cause phenolphthalein to change color. Because Mountain Dew contains a yellow dye the solution will become salmon colored (or pink grapefruit or peach-orange depending on how you perceive the color). The actual tone of the color is not important: The first change in color that persists for about 30 seconds means the titration is complete. 10. Read the level of NaOH in the burette and record the value as the final volume in the Data Table 11. Discard the neutralization mixture in the 250-ml Erlenmeyer flask. (Recover the stir bar first if you used one another magnetic stirring bar inserted into the end of a piece of plastic tubing makes this easy and keeps your fingers clean.) Rinse the flask with water to remove all traces of base. 12. Refill the burette with NaOH solution of the same concentration used for the last titration. Don't forget: use a funnel! and wear eye protection! 13. Repeat steps 1-11 for the next titration.