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|Three solutions are combined in alphabetical order. |
Solutions A and B produce a red solution. Adding solution C after this turns the solution milky white, then blue after a time.
The hydrochloric acid in solution B turns the 2,4,2',4',4"-pentamethoxytriphenyl methanol (an indicator) red. The addition of solution C causes the pH to increase due to the formation of OH- ions in the IO4- oxidation of S2O32-.
2 S2O32- (aq) + IO4- (aq) + H2O (l) --> S4O62- (aq) + IO3- (aq) + 2 OH- (aq)
When the indicator turns colorless again, the milky-white suspension of Cd(IO4)2+ becomes apparent. The further increase in pH triggers another indicator (thymolphthalein), turning the solution blue.
This material is based upon work supported by the National Science Foundation under Grant Number 1246120