The Roy G Biv Clock Reaction
Publication No. 12028
Take seven different dry chemical mixtures and add each to a separate beaker. Pour a clear liquid into each beaker and, in less than a minute, a rainbow of colors appears.
(for each demonstration)
Isopropyl alcohol, (CH3)2CHOH, 28%, 140 mL*
Formaldehyde, HCHO, 37% solution, 7 mL*
Dry mixture #1, 1 g*†
Dry mixture #2, 1 g*†
Dry mixture #3, 1 g*†
Dry mixture #4, 1 g*†
Dry mixture #5, 1 g*†
Dry mixture #6, 1 g*†
Dry mixture #7, 1 g*†
Water, distilled or deionized
Beakers, 400-mL, 7
Erlenmeyer flask, 2000-mL
Graduated cylinder, 10-mL
Graduated cylinder, 25-mL
Stirring rods, 7
*Materials included in kit.
Formaldehyde is a known carcinogen. Formaldehyde is a strong irritant; avoid breathing vapor and avoid skin contact. Formaldehyde is highly toxic by ingestion, inhalation and skin absorption. The use of formaldehyde in this demonstration does not present an unnecessary risk. Use a fume hood to prepare solution. Sodium sulfite is moderately toxic; possible skin irritant. Sodium bisulfite is slightly toxic; severe irritant to skin and tissue as an aqueous solution. meta-Nitrophenol is moderately toxic by ingestion, inhalation and skin absorption; body tissue irritant. Phenolphthalein acts as a laxative upon ingestion; a body tissue irritant. Avoid body tissue contact. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.
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 reaction products may all be disposed of according to Flinn Suggested Disposal Method #26b. The formaldehyde solutions may be disposed of according to Flinn Suggested Disposal Method #2. Sodium sulfite/sodium bisulfite dry powder mixtures and solutions may be disposed of according to Flinn Suggested Disposal Method #12b.
Formaldehyde solution: Dilute 7 mL of the 37% formaldehyde solution with 1.7 liters of deionized water in a 2000-mL Erlenmeyer flask. Stir the solution. The final formaldehyde solution concentration is approximately 0.05 M. Prepare this solution at least 2 hours before use in the demonstration.
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Constructing explanations and designing solutions
Disciplinary Core IdeasMS-PS1.B: Chemical Reactions
HS-PS1.B: Chemical Reactions
Crosscutting ConceptsSystems and system models
Stability and change
HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
Answers to Questions
In this clock reaction, formaldehyde reacts with sulfite ions to form hydroxymethyl sulfonate ions and hydroxide ions.
The bisulfite ion is a weak acid and it is in solution with its conjugate base, the sulfite ion, setting up a buffer condition in the solution.
Initially, the solution is slightly acidic, with a pH of approximately 6.4. As the reaction proceeds (Equation 1), sulfite ions are consumed and hydroxide ions are produced. This reduction in sulfite ion concentration causes a shift to the right in Equation 2, producing sulfite ions and hydronium ions (H3O+). The hydronium ions, in turn, react with the hydroxide ions to produce water.
This buffering action holds the pH of the solution relatively constant until all the bisulfite ions have been consumed. The hydroxide ion concentration then builds up causing a rapid rise in solution pH.
The color changes of the indicators in the solution all occur as the solution pH changes from 7 to 10. Phenolphthalein changes from colorless to red-purple in the pH range of 8.0–9.6, thymolphthalein changes from colorless to blue in the pH range of 9.3–10.6, and meta-nitrophenol changes from colorless to yellow in the pH range of 6.8–8.6. The seven colors of the final solutions are a result of the different combinations of these three indicators.
Special thanks to Steve Spangler, Director of the National Hands-On Institute, Regis University, Denver, CO, for providing the idea and procedure for this demonstration.