A solution of iodine and potassium iodide is dripped on to a substance and if it contains starch, a deep blue colour will materialise. Here's the science bit! Starches contain a sugar called ...

I. The reaction between iodide and hydrogen peroxide produces triiodide. The triiodide ions are reduced back to iodide by thiosulfate at a much faster rate, until the thiosulfate is consumed. Then the ...