Water to Grape Juice to Milk

Introduction

Magically turn water to grape juice to lemonade to 7-Up^® to milk to finally—after consuming all that, you’ll surely need— Pepto-Bismol^®!

Concepts

• Acids and bases
• Solubility and precipitates

Materials

Safety Precautions

Sulfuric acid solution is severely corrosive to eyes, skin and other tissue. Sodium hydroxide solution is corrosive and a body tissue irritant. Barium nitrate solution is a strong oxidizer and moderately toxic by ingestion. Phenolphthalein solution is an alcohol-based solution; it is flammable and moderately toxic by ingestion. Avoid body tissue contact with all solutions. 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 final solution can be flushed down the drain with plenty of water according to Flinn Suggested Disposal Method #26b. Remaining amounts of the reagents included in the kit can be saved for later use or disposed of according to the appropriate Flinn Suggested Disposal Methods.

Prelab Preparation

Prior to audience arrival, treat and label six glasses or beakers as follows:

Glass 1—Water: 200 mL of distilled or deionized water and 3–4 drops of 1% phenolphthalein solution
Glass 2—Grape Juice: 10 drops of 0.1 M NaOH solution
Glass 3—Lemonade: 1.5 mL of 9 M H₂SO₄ solution
Glass 4—7-Up^®: 1 g (½ scoop) of NaHCO₃ and 1 pipet (2–3 mL) of water; swirl gently
Glass 5—Milk: 3 pipets (7–9 mL) of saturated Ba(NO₃)₂ solution
Glass 6—Pepto-Bismol^®: 2 pipets (5–6 mL) of 6 M NaOH solution (must be sufficient to overcome the acid)

Procedure

1. Begin with a story (if you like) as glass 1 (“water”) is held up. Phenolphthalein is colorless in a neutral environment.
2. Pour the contents of glass 1 into glass 2. A color forms. Phenolphthalein is pink in a basic environment.
3. Pour the contents of glass 2 into glass 3. The pink color disappears and the solution is once again colorless. Phenolphthalein is colorless in an acidic environment.
4. Pour the contents of glass 3 into glass 4. The acidic solution reacts with the sodium bicarbonate to create bubbles of carbon dioxide gas.
5. Wait for the fizzing to stop and then pour the contents of glass 4 into glass 5. The clear solution turns a cloudy white (“milk”). The white precipitate is a result of the barium ions interacting with the sulfate ions to form barium sulfate. 6. Pour the contents of glass 5 into glass
6. The cloudy white mixture turns to a cloudy light pink mixture (“Pepto-Bismol”). The pink color forms because phenolphthalein is pink in a basic environment.
   {11832_Procedure_Figure_1}

Student Worksheet PDF

11832_Student1.pdf

Teacher Tips

• There are enough chemicals to perform the demonstration 14 times. This allows the demonstration to be shown to each class twice—once for entertainment and a second time to discuss the chemistry and reactions occurring. Plus there is plenty for practice and preparation purposes.
• Be creative and dramatic with this demonstration for more effect. Use a variety of glasses, such as a water goblet for the water and a juice glass for the grape juice. A few drops of yellow food coloring and perhaps a lemon slice in glass 3 will help with the lemonade.
• The volume of a Beral-type pipet is approximately 2.5–3 mL. Volumes given are approximate and the amounts indicated are for a final solution volume of 200 mL. The amounts can be scaled up or down if a different amount of solution is desired, depending on the size of glasses used. Check the volumes of the chosen glasses and practice before performing this demonstration to an audience.
• The small volumes of liquid in the glasses or beakers will almost certainly not be spotted by the audience.
• This makes an impressive introductory demonstration for your chemistry class. One teacher’s idea—Present the demo to the class as an entertaining activity, going through the motions while telling a story about a chemistry department dinner party, with no explanations as to what types of reactions are taking place. Repeat the demonstration later in the year during the acid/base unit. This time, discuss the reactions occurring inside the glasses. To begin, only share information with the students about the contents of the first glass. Have them “guess” the contents of each consecutive glass that would be consistant with observations. Then reveal what was in each glass and have students write the reactions.
• You may have seen this demonstration done as water to wine to a martini to champagne to milk to Pepto-Bismol^®.

Answers to Questions

1. Draw the setup for this demonstration. Label each glass with its contents and note the appearance the solution had in each glass.
   {11830_Answers_Figure_2}
2. Explain the color change, and any other observations, for each glass.

   Glass 1—Water is neutral. Phenolphthalein, an acid–base indicator, is colorless in a neutral environment.
   Glass 2—Sodium hydroxide is a base. Phenolphthalein is pink in a basic solution.
   Glass 3—Sulfuric acid is an acid. Phenolphthalein is colorless in an acidic solution.
   Glass 4—The acidic solution reacts with the sodium bicarbonate to create bubbles of carbon dioxide gas.
   Glass 5—Barium ions react with sulfate ions to form barium sulfate, which is a white precipitate.
   Glass 6—Sodium hydroxide is a base. Phenolpthalein is pink in a basic solution.

3. Write a balanced chemical equation for the reactions that occurred in Glass 4 (“7-Up”) and Glass 5 (“milk”).

   HCO₃^–(aq) → CO₃^2–(aq) + H⁺(aq) → CO₂(g) + H₂O(l)
   BA²⁺(aq) + SO₄^2–(aq) → BaSO₄(s)

Discussion

Phenolphthalein indicator solution is an acid–base indicator that remains colorless in an acid solution but turns from colorless to pink at about pH of 9, having a distinct pink color in a basic solution.

Following is a summary of what is occurring in each glass
Glass 1: Phenolphthalein + Water → Colorless soultion
Glass 2: Phenolphthalein + Base → Pink Solution
Glass 3: Phenolphthalein + Acid → Colorless solution
Glass 4: HCO₃^–(aq) → CO₃^2–(aq) + H⁺(aq) → CO₂(g) + H₂O(l) Fizzing
Glass 5: Ba²⁺(aq) + SO₄^2–(aq) → BaSO₄(s) White precipitate
Glass 6: Phenolphthalein + Base → Pink and cloudly