Chemical Concepts Demonstrated: reversible reactions, equilibrium, complex reaction mechanisms
|Three solutions are combined in alphabetical order.
The resulting solution turns fron amber to blue-black. The blue slowly fades to colorless, and the reaction begins again. During the course of the reaction, bubbles are evolved.
Explanations (including important chemical equations):
Although the complete mechanism is uncertain, the reaction is believed to be an indirect route to decomposing H2O2 into H2O and O2, related to the H2O2/IO3- oscillating reation. If so, the amber color results from the production of I2 in the absence of I -, while the blue color results from the simultaneous presence of both I2 and I - leading to the blue starch-I3- complex. The bubbles are oxygen gas. The following steps have been proposed:
5 H2O2 (aq) + I2 (aq) --> 2 HIO3 (aq) + 4 H2O (l)
5 H2O2 (aq) + 2 HIO3 (aq) --> 5 O2 (g) + I2 (aq) + 6 H2O (l)
The functions of the malonic acid and the manganese ion may be to increase the size and frequency of the I2 and I - fluctuations.