The iodine clock reaction is a popular chemical reaction demonstrating chemical kinetics. When iodine is reacted with starches or sodium thiosulfate, it forms a dark blue color, almost black. In this reaction, either sodium, potassium or ammonium persulfate are combined with iodine. Iodine is reduced and forms the dark color seen in the image above. However, contrary to the above image, the reaction isn't actually gradual. It actually happens immediately, with a barely visible intermediate step.
The reaction goes something like this: I2(aq) + 2S2O3.2- (aq) → 2I- (aq) + S4O6.2- (aq)
This reaction can actually be reversed if you add the right amount of dithionite.
Below is a video of the process, if you would like to see how quickly it happens.
The reaction goes something like this: I2(aq) + 2S2O3.2- (aq) → 2I- (aq) + S4O6.2- (aq)
This reaction can actually be reversed if you add the right amount of dithionite.
Below is a video of the process, if you would like to see how quickly it happens.