Which Soda Is the Most Acidic?

Name: ______Date: ______

Purpose: In this lab you will perform a micro-titration experiment to compare the relative acidity of several types of sodas. By adding NaOH to soda containing phenolphthalein it can be determined how much of that base is needed to neutralize the acid in the soda.

Materials: Test Tubes, Test Tube Rack, 10mL Graduated Cylinder, Various Sodas, 0.2M NaOH, Phenolphthalein, Pipettes

Pre-Lab:

1. What ion do all acids contain? ______What ion do all bases contain? ______

2. Neutralization is when those two ions combine in a 1 to 1 ratio. What molecule is the result of that?

3. What color is phenolphthalein in an acid? ______

What color is it in a base? ______

Procedure:

1. Use a pipette to measure exactly 2mL of one of the sodas and pour it into a test tube. 2. Add 2 drops of phenolphthalein to the test tube containing the soda. 3. Carefully add the NaOH to the acid, 1 drop at a time, counting each drop. Notice that the color that appears will disappear if the test tube is swirled. 4. Continue adding drops of NaOH until the phenolphthalein color does not disappear when swirled. Record the number of drops of NaOH that it took to neutralize the acid in the data table below. 5. Repeat steps 1-4 for all of the types of soda. 6. Dispose of the contents of the test tubes in the sink and rinse out the test tubes well.

Data: Soda Drops of NaOH Old Sprite New Sprite New Mountain Dew Old Mountain Dew Old Crystal Pepsi Data Analysis:

1. Construct a bar graph of the number of drops of iodine used to reach the titration endpoint of each beverage. Color each bar a different color. 25 24 23 22 21 20 19 18 17 16 15 14 Drops of 13 NaOH Needed To 12 Neutralize 11 Soda Acid 10 9 8 7 6 5 4 3 2 1 Old New Old New Old Sprite Mountain Mountain Crystal Sprite Dew Dew Pepsi

2. What is the relationship between the acidity of the soda and the number of drops of NaOH needed to neutralize it? 3. Which soda(s) contained the most acid?

4. Which soda(s) contained the least acid?

Conclusion Questions:

1. Based on your results, which soda(s) would have the lowest pH? Explain how you know.

2. We tested different brands of soda and also old and new samples. State two conclusions that you can make about how those variables affect the acidity of soda. Back up your conclusions by citing specific data.

3. I have a soda with a pH of 3 and I combine it with some baking soda (a base). This causes the hydrogen ion concentration of the soda to decrease by 1000. Have I added the right amount of baking soda to exactly neutralize the soda? (Show the calculations needed to answer this.)