Orange Juice to Strawberry Float

Introduction

It’s big, it’s colorful, it’s messy, and it’s chemistry! Watch as the “orange juice” in a beaker changes into a foamy “strawberry float.” What a great way to introduce acids and bases to your students!

Concepts

• Acids and bases
• Acid–base indicators

Materials

Safety Precautions

Hydrochloric acid (3 M) is moderately toxic by ingestion and inhalation; it is corrosive to body tissues, especially to the eyes. Methyl orange solution (0.2%) is slightly toxic by ingestion. Alconox^® and sodium bicarbonate are irritants, especially to the eyes. This demonstration rapidly generates a foamy mixture which may spray in all directions. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The resulting mixture should be diluted with water, neutralized, and flushed down the drain with plenty of water according to Flinn Suggested Disposal Method #24b.

Procedure

1. Place a very large tray on the demonstration table.
2. Add approximately 300 mL of tap water to a 2-L beaker.
3. Add 50 g sodium bicarbonate and 50 g Alconox^® to the 2-L beaker. Stir the solution with the long stirring rod. All of the solid may not dissolve.
4. Add 100 mL of 0.2% solution methyl orange indicator to the beaker containing the sodium bicarbonate and Alconox. Stir. The resulting solution should look somewhat like orange juice; however, the orange solution is thicker and darker in color than actual orange juice.
5. Pour approximately 270–280 mL of 3 M hydrochloric acid into a 600-mL beaker.
6. Place the beaker containing the sodium bicarbonate mixture in the center of a very large tray or in the sink or in an aquarium.
7. Wearing chemical splash goggles, quickly but carefully, add the 270–280 mL of HCl all in one pour to the first beaker. Stand back as the mixture will immediately erupt out of the beaker.
8. Note the color change of the mixture. The solution will look like a strawberry float, but after some time, parts of the solution will turn yellow.

Student Worksheet PDF

12925_Student1.pdf

Teacher Tips

• There are enough materials provided in this kit to perform the demonstration seven times.
• This demonstration is very messy and produces over 13 liters of soap bubbles that may still contain small amounts of hydrochloric acid. Please practice this demonstration before performing it in front of your students. All persons watching the demonstration should be wearing chemical splash goggles. All amounts can be cut in half for a safer and less messy (yet less dramatic) alternative.
• This demonstration can also be performed in a 1-L or 3-L beaker. It is advised not to use an Erlenmeyer flask or a graduated cylinder as excessive splattering will erupt out of the narrow mouth.
• It is possible to substitute 75 g or 25 g of Alconox^® (rather than 50 g) for more or less foam, respectively. Liquid dish detergent also works (about three healthy squirts) but gives a lower quality foam. A less foamy reaction will occur using 25 g of sodium bicarbonate (rather than 50 g) and 1 M hydrochloric acid (rather than 3 M) with the same amount of soap (50 g).

Answers to Questions

1. Describe what happened in this demonstration. Make sure to mention all the chemicals used.

   3 M hydrochloric acid was added to a large beaker containing a solution of sodium bicarbonate, soap, and methyl orange, an acid–base indicator. The solution, which was originally the color of orange juice, turned red and a great deal of foaming was produced.

2. Write a chemical equation for the reaction that occurred when hydrochloric acid was added to the mixture inside the large beaker.

   NaHCO₃(aq) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)

3. What product of this reaction and what chemical present in the original mixture were responsible for the foaming? Explain.

   The carbon dioxide gas (CO₂) produced by the reaction between the hydrochloric acid and sodium bicarbonate, along with the soap, were responsible for the foaming. The CO₂ became trapped in the soap bubbles from the detergent, causing an abundance of soap bubbles.

4. What chemical was responsible for the color change? Explain.

   The methyl orange indicator was responsible for the color change. Methyl orange is red in an acid and yellow-orange in a base, and thus when the hydrochloric acid was added, the color of the solution changed to a strawberry red.

Discussion

The sodium bicarbonate reacts with the hydrochloric acid in a neutralization reaction to produce sodium chloride, water and carbon dioxide gas according to the following equation:

Methyl orange is an acid–base indicator that turns from a yellow-orange color at pH 4.4 to a red color at pH 3.0. The initial basic solution has a deep orange color. The intensity of the yellow-orange solution is due to the high indicator concentration. Upon adding the acid, the pH drops and a strawberry red color forms. One of the products of this neutralization reaction is carbon dioxide gas, which is rapidly produced and becomes trapped in the soap bubbles. Over 13 liters of CO₂ gas is produced in this reaction resulting in an abundance of soap bubbles.

References

Special thanks to Ken Runkle, Carlinville High School, Carlinville, IL, for bringing this demonstration to our attention. Ken saw this demonstration performed by Robert J. Harris, Morristown High School, Morristown, NJ, at Fairleigh-Dickenson University during the summer of 1991.