Briggs-Rauscher Reaction

Materials

• 30% H2O2
• Soluble starch
• KIO3
• 1 M H2SO4
• MnSO4·H2O
• Malonic acid
• Water
• Stir plate and stir bar
• Graduated cylinders (3)
• Large beaker
• ~200 mL beakers (for preparation of solutions)
• Hot plate (for preparation)

Safety Precautions

• Please read the Liquid Chemical section of the Demonstration Safety page before performing this demonstration.

This demonstration requires: safety glasses or goggles and rubber or latex gloves.

Demonstration

Preparation

• Prepare 100 mL of 9% H2O2 by diluting 30 mL of 30% H2O2 with 70 mL of deionized H2O in a graduated cylinder.
• Prepare an acidified 0.2 M KIO3 solution by adding 10 mL of 1.0 M H2SO4 to 80 mL of deionized water. Dissolve 4.3 g KIO3 in this solution and dilute to 100 mL in a graduated cylinder.
• Prepare starch solution by dissolving 0.1 g of soluble starch in 90 mL of boiling water. When cool, add 1.5 g malonic acid, 0.4 g MnSO4·H2O, stir and dilute to 100 mL in a graduated cylinder.

Presentation

• Add the H2O2 solution to a clean beaker fitted with a stir bar. Next, add the KIO3 solution and let the solutions mix thoroughly. Then, add the starch solution to the beaker, keeping the stir rod spinning. Upon addition of the final solution, bubbles should appear. The solution will turn yellow then blue,

then colorless. This reaction should oscillate for 5-10 minutes.

Why This works

This is what is called on oscillating reaction. The color changes view correspond to an increased concentration in one of the different states of Iodine in solution: yellow for I2, blue for starch-iodine complex, and colorless for I1-. The Briggs-Rauscher reaction can be summarized by two chemical reactions: IO31- + 2 H2O2 + H1+ ® HOI + 2 O2 + 2 H2O and HOI + CH2(CO2H)2 ® ICH(CO2H)2 + H2O

When the reaction begins, the solution becomes yellow as I1- (generated from reaction of HOI with H2O2, not shown) reacts with HOI under acidic conditions to produce I2. The solution suddenly changes to dark blue as a buildup of I1- reacts with I2 in the presence of starch to generate the pentaiodide ion (I51-) which is encased in the amylose present in solution. The reaction proceeds by consuming I2 at a rate greater than it is being produced thus removing the presence of I51- and increasing the concentration of I1- (colorless). The oscillations continue until malonic acid or IO31- is completely consumed.

Disposal

Dispose of remaining liquids in an appropriately labeled liquid chemical waste container.

The procedure and explaination used can be located at https://projects.ncsu.edu/project/chemistrydemos/Kinetics/BriggsRauscher.pdf. For a more-complete list of chemical reactions, please see https://www.chem.tamu.edu/roadshow/assets/docs/demos/OcillationgColors.pdf. Shakhashiri, B. Z. In Chemical Demonstrations: A Handbook for Teachers of

    Chemistry; The University of Wisconsin Press: 1985; Vol. 2, p 248-256