The Briggs-Rauscher reaction is an oscillating clock chemical reaction that cycles from clear, amber, to deep blue several times before finally ending as a blue-black mixture. It is one of the most popular chemistry demonstrations because it’s easy and reliable and because it illustrates complex reaction dynamics and non-equilibrium thermodynamics.
Briggs–Rauscher Reaction Quick Facts
- Type: Oscillating clock reaction
- Color changes: Clear → Amber → Blue → Repeats
- Number of cycles: Typically 10–20, up to 40
- Main reactants: Hydrogen peroxide, iodate, malonic acid
- Mechanism: Competing radical and non-radical pathways
- Safe for home use with precautions and neutralization
How to Do the Briggs-Rauscher Reaction
Doing the Briggs-Rauscher reaction is simple. You prepare three solutions and then mix them to initiate the reaction.
Note: For best results, prepare the solutions a short while before the reaction (or at least store them away from light). Ultraviolet radiation from sunlight or fluorescent lights decomposes some reactants or causes them to react with one another, reducing the effect.
Materials
You need the following chemicals and materials:
- 43 g Potassium iodate (KIO3)
- Sulfuric acid (H2SO4)
- 15.6 g malonic acid (HOOCCH2COOH)
- 3.4 g manganese sulfate monohydrate (MnSO4 . H2O)
- 4 g vitex starch (modified starch)
- 30% hydrogen peroxide (H2O2)
- Distilled water
- 1-L beaker
- Flasks or beakers for mixing
- Stirring plate
- Magnetic stir bar
Prepare the Solutions
Make the following three solutions:
- Solution A: Iodate and Acid – Place 43 g potassium iodate in about 800 ml distilled water. Add 4.5 ml sulfuric acid and stir the solution until the potassium iodate dissolves. Dilute to 1 L.
- Solution B: Malonic Acid and Starch – Stir 15.6 g malonic acid and 3.4 g manganese sulfate monohydrate into about 800 ml of distilled water. Add 4 g vitex starch. Stir until the solids dissolve. Dilute to 1 L.
- Solution C: Hydrogen Peroxide – Dilute 400 ml of 30% hydrogen peroxide to 1 L.
The concentration of the solutions is not critical. However, changing concentration affects the intensity of the colors and the rate of the “clock”.
How to Perform the Briggs-Rauscher Reaction
- Place a stirring bar in a 1-L beaker and set the beaker on a stirring plate.
- Pour 300 ml each of solutions A and B into the beaker.
- Turn on the stirring plate and adjust its speed so a large vortex forms.
- Add 300 ml of solution C.
Note: Be sure solutions A and B are fully mixed before adding solution C or else the reaction will not work as well.
Troubleshooting Tips
- Reaction too slow → increase temp
- No color change → bad peroxide or contaminated solutions
- Weak colors → increase starch or iodate concentration
Safety and Disposal
- The chemicals include irritants and oxidizing agents. Do not touch the chemicals or solutions.
- Wear gloves and goggles. Ideally perform the reaction under a fume hood. Otherwise, do the reaction in a well-ventilated space.
- For disposal, add about 10 g sodium thiosulfate to neutralize the iodine to iodide. Stir until the mixture becomes colorless. This reaction is exothermic, so expect it to get hot. Once cool, wash the neutralized mixture down the drain with water.
How the Briggs-Rauscher Reaction Works
While the specific details of the reaction are somewhat complicated, the overall reaction is as follows:
IO3– + 2 H2O2 + CH2(CO2H)2 + H+ → ICH(CO2H)2 + 2 O2 + 3 H2O
Two processes occur in this reaction, with each process containing many individual reactions.
- A non-radical process involves slow consumption of free iodine by malonic acid. This process occurs in the presence of iodate.
- A radical process involves manganese and free radicals, auto-catalytically converting iodate and hydrogen peroxide into iodine and oxygen.
The cycling that makes it a clock reaction works like this:
The radical process only occurs when iodide concentration is low. Initially, iodide is low, so the radical process forms free iodine. At the same time, the non-radical process generates iodide. When the non-radical process makes enough iodide, it inhibits the radical process. The radical process continues consuming iodine and iodide until the concentration falls low enough for the radical process to start again. The cycling continues until the reactants are consumed.
The increasing amber color comes from production of free iodine by the radical process. When the radical process stops, the increase in iodide ion forms a blue complex with starch. Since the non-radical process continues consuming iodine, eventually the blue color fades and the solution turns clear.
Interesting Variations
- Using diluted solutions results in more cycles and faster cycles. However, the colors are weaker.
- Replacing malonic acid with other substrates, such as acetylacetone (CH3COCH3COCH3) or acetone (CH3COCH3) changes the oscillation pattern of the clock reaction.
- Normally, the Briggs-Rauscher reaction eventually stops. However, an ongoing cycle results from using a continuous flow stirred tank reactor (CSTR) that adds reagents while removing excess liquid.
- Replacing starch with a fluorescent dye produces a reaction that glows under ultraviolet (black) light.
Briggs-Rauscher Reaction FAQs
How long does the Briggs-Rauscher reaction last?
The number of cycles depends on temperature, whether or not you stir the solution, concentration, and light exposure. Typically, the reaction cycles between 10 and 20 times. Diluting the reactants makes the reaction cycle more rapidly, potentially up to 40 times.
Can you do the Briggs-Rauscher reaction at home?
You can do the Briggs-Rauscher reaction at home, but you’ll need to order the chemicals online. It’s safe to wash the waste down the drain after it is neutralized, but keep in mind the reactants are irritants. Unless you are specifically exploring clock reactions, it’s easier and more economical to do the “water into wine” or “blue bottle” reaction.
More Color Change Chemical Reactions
The Briggs-Rauscher reaction is the most common clock reaction. However, there are several other interesting color change chemical reactions.
- Christmas chemistry reaction: This is a red to green clock reaction, perfect for the winter holidays.
- Water into wine or water into blood reaction: This is a clear to red color change reaction.
- Gatorade and drain cleaner reaction: This color change reaction uses everyday materials, making it suitable for home school experiments.
- Blue bottle reaction: This redox reaction changes from blue to clear. While not a clock reaction, it is repeatable.
- Hot and cold reaction: A solution changes colors from pink to clear and back again.
- Vanishing Valentine: A solution changes from clear to pink and returns to its colorless state.
Comparison of Clock Reactions
| Clock Reaction | Color Change | Main Reactants | Mechanism Type | Repeating Cycles | Notes |
|---|---|---|---|---|---|
| Briggs–Rauscher | Clear → Amber → Blue → … | H₂O₂, iodate (KIO₃), malonic acid, Mn²⁺, starch | Radical + Non-radical oscillation | Yes (10–40 cycles) | Most dramatic; cycles several times; sensitive to light and concentration |
| Belousov–Zhabotinsky | Orange/Red ↔ Blue/Green | Malonic acid, cerium or ferroin, bromate | Nonlinear chemical oscillator | Yes (many cycles) | First discovered oscillating reaction; models biological rhythms |
| Iodine Clock | Clear → Dark Blue (sudden) | Iodide, hydrogen peroxide, starch | Redox time-delay | No (single jump) | Classic clock reaction; used to study kinetics |
| Vitamin C Clock | Clear → Blue (sudden) | Iodine, vitamin C (ascorbic acid), hydrogen peroxide | Redox time-delay | No (single jump) | Safer for classroom use; color change delay depends on vitamin C concentration |
| Landolt Reaction | Colorless → Blue/Black | Iodide, iodate, sulfurous acid | Redox time-delay | No (single jump) | First clock reaction (1886); similar in principle to iodine clock |
| Blue Bottle | Blue ↔ Clear (repeatable) | Glucose, NaOH, methylene blue | Redox with air (oxygen) | Yes (with shaking) | Not a true clock reaction; requires agitation to repeat |
| Chemical Traffic Light | Red ↔ Yellow ↔ Green | Glucose, NaOH, indigo carmine | Redox with pH-dependent dye | Yes (manual cycling) | pH and redox changes induce color cycling; often used in bottle demonstrations |
| Vanishing Valentine | Clear → Pink → Clear | Phenolphthalein, NaOH, glucose | Redox + pH change | Yes (if reset) | Depends on oxygen levels; often used for holiday-themed demos |
Notes:
- “Repeating Cycles” refers to whether the reaction oscillates automatically or requires resetting (e.g., shaking or adding more reactants).
- Most true oscillating reactions involve feedback mechanisms and occur far from equilibrium.
- Clock reactions often use starch–iodine complexes for visual contrast.
References
- Belousov, B. P. (1958). “A Periodic Reaction and Its Mechanism”. Sbornik Referatov po Radiatsionni Meditsine. Medgiz, Moscow.
- Bray, W. C. (1921). “A Periodic Reaction in Homogeneous Solution and Its Relation to Catalysis”. J. Am. Chem. Soc. 43 (6): 1262–1267. doi:10.1021/ja01439a007
- Field, R. J. (1972). “A Reaction Periodic in Time and Space”. J. Chem. Educ. 49: 308. doi:10.1021/ed049p308
- Furrow, Stanley D.; Cervellati, Rinaldo; Amadori, Giovanna (2002). “New Substrates for the Oscillating Briggs–Rauscher Reaction”. J. Phys. Chem. A. 106 (24): 5841–5850. doi:10.1021/jp0138779
- Shakhashiri, B. Z. (1992) Chemical Demonstrations: A Handbook for Teachers of Chemistry Vol. II. University of Wisconsin Press, Madison, WI.