Reacciones encadenadas: del reloj de yodo al arco iris químico

To motivate students to learn chemistry, we present an experience which will catch their attention and can be useful to introduce several chemical concepts in the classroom. It consists in linking the reduction reaction of potassium iodate by sodium bisulfite in the presence of starch with another one in which colored indicators solutions appear when they change from an acidic to a basic medium.In seven glasses containing a colorless solution, another also colorless solution is added. The content of the glasses suddenly and successively turns to dark blue. By pouring a third clear solution in the glasses, dark color vanishes and the colors of the rainbow appear producing an eye-catching effect.