Fizzy

Fizzy Drinks: Stoichiometry You Can Taste

by Brian Rohrig, Journal of Chemical Education

Introduction

There is a unique product on the market known as Fizzies, which enables you to make your own carbonated beverage by dropping a tablet into water. The ensuing chemical reaction produces carbon dioxide gas, which causes the drink to be carbonated (hence the "fizz"). The same reaction occurs in Alka-Seltzer antacid tablets, effervescent denture cleaners and the popular baking soda and vinegar volcano science experiment. In addition to color and flavoring, Fizzies contain citric acid (H₃C₆H₅O₇) and baking soda (NaHCO₃). When water is added they react, forming sodium citrate, water and carbon dioxide gas. In this activity, you will use this reaction to make your own carbonated beverage.

Materials

5 full size cups tasting cups (one per group member)

4 paper muffin cups plastic spoon

marker balance

cup measure aspartame sweetener

packet of powdered drink mix citric acid

baking soda water

Safety

Do NOT do this activity in the laboratory or use any laboratory equipment other than a balance. The balance should be removed from the laboratory to a classroom or kitchen and should be cleaned thoroughly before using. Solids are weighed using clean paper muffin cups. If any solid is spilled on the balance or balance pan, the solid must be discarded. Taste only very small amounts of the beverages in cups B, C, and D.

Procedure

1. Read the instructions on a package of unsweetened powdered drink mix. Determine the mass of drink mix and the amount of sugar and water for a single serving. Determine the amount of aspartame sweetener that replaces this amount of sugar. (The sweetener package should include a sweetness conversion table for sugar.)

Helpful conversions:

1 cup = 8 fluid ounces

1 cup = 16 tablespoons

1 tablespoon = 3 teaspoons

One serving--

water: _______________ sugar: _______________

drink mix: _____________ artificial sweetener: ______________

2. Label four paper muffin cups: "drink mix," "sweetener," "citric acid," and "baking soda." Label five plastic cups A through E.

3. Place the muffin cup labeled "drink mix" on the balance and tare the balance. Weigh the quantity of drink mix for a single serving and transfer it to cup A. Repeat for cups B through E until all cups have the same amount of drink mix.

4. Add the amount of sweetener for a single serving to each of the cups, using the balance and muffin cup labeled "sweetener" if necessary.

5. Add the quantity of cold water for a single serving to the cup labeled A. Stir with a plastic spoon until all solid has dissolved. Taste and record your observations. Keep this cup as your control. It may be helpful to make a table in which to record your tasting observations for each cup.

6. Using the muffin cup labeled "citric acid" and the balance, add a measured amount of citric acid to the cup labeled B (1-5 grams...it's up to you how much you use, just be sure to record the number, preferably somewhere in your tasting observations table). Add the quantity of cold water for a single serving, stir, taste only a very small amount, record observations, and discard.

7. Using the muffin cup labeled "baking soda" and the balance, add a measured amount of citric acid to the cup labeled C (1-5 grams...it's up to you how much you use, just be sure to record the number, preferably somewhere in your tasting observations table). Add the quantity of cold water for a single serving, stir, taste only a very small amount, record observations, and discard.

8. Using the appropriate muffin cups and the balance, measure amounts of both baking soda and citric acid (no more than 5 grams each) and add to the cup labeled D. Add the quantity of cold water for a single serving, stir, taste only a very small amount, record observations, and discard.

9. If time permits, experiment with different amounts of citric acid and baking soda (no more than 5 grams of each). Can you make a good-tasting beverage? Taste only small amounts of each and be sure to record your findings!

10. Write the balanced chemical equation for the reaction between citric acid and baking soda. (see the introduction above and your polyatomic ion sheet for help with writing the formulas for the reactants and products). Using stoichiometry, determine how much citric acid is required to react completely with 1.00 g of baking soda. Have your instructor check your work before you proceed.

11. With your instructor's approval, weigh 1.00g of baking soda and the amount of citric acid calculated in step 10. Add these amounts to the cup labeled E. Add the quantity of cold water for a single serving, stir, and taste, recording your observations. Compare the cup A. If you wish, you may drink the contents of cups A and E, but pour all others down the drain after you taste a small amount.

Questions

1. Why do citric acid and baking soda not react until water is added?

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2. Why is fizzing observed in cup C?

3. How will the drink taste if too much citric acid is added? How will it taste if too much baking soda is used?

4. Why do commercial Fizzies tablets used aspartame sweetener instead of sugar? (hint: consider step 1 of the procedure)

5. What volume of carbon dioxide gas was produced during the reaction from the drink in step 11?

6. What are some other practical uses of stoichiometry?