IO3- + 2 H2O2 + CH2(CO2H)2 + H+ --> ICH(CO2H)2 + 2 O2 + 3 H2O
The reaction can be broken into two components :
IO3- + 2 H2O2 + H+ --> HOI + 2 O2 + 2 H2O
This reaction can occur by a radical process which is turned on when I- concentration is low, or by a nonradical process when the I- concentration is high. Both processes reduce iodate to hypoiodous acid. The radical process forms hypoiodous acid at a much faster rate than the nonradical process.
The HOI product of the first component reaction is a reactant in the second component reaction:
HOI + CH2(CO2H)2 --> ICH(CO2H)2 + H2O
This reaction also consists of two component reactions:
I- + HOI + H+ --> I2 + H2O
I2CH2(CO2H)2 --> ICH2(CO2H)2 + H+ + I-
The amber color results from the production of the I2. The I2 forms because of the rapid production of HOI during the radical process. When the radical process is occurring, HOI is created faster than it can be consumed. Some of the HOI is used while excess is reduced by hydrogen peroxide to I-. The increasing I- concentration reaches a point at which the nonradical process takes over. However, the nonradical process does not produce HOI nearly as fast as the radical process, so the amber color begins to clear as I2 is consumed more quickly than it can be created. Eventually the I- concentration drops low enough for the radical process to restart so the cycle can repeat itself.
The deep blue color is the result of the I- and I2 binding to the starch present in the solution.