"Chemical Traffic Light" experiment

Due to this reactions, liquid will turn green, then red and then yellow

The chem­i­cal traf­fic light is a stun­ning col­or­ful re­ac­tion! The ex­per­i­ment in­volves chang­ing col­ors with an in­di­ca­tor – in­di­go carmine in an al­ka­line so­lu­tion of glu­cose. The al­ka­line so­lu­tion of glu­cose is poured into a so­lu­tion of in­di­go carmine, and we ob­serve a grad­u­al change of col­or: blue – green – red – yel­low. We can re­verse the re­ac­tion sim­ply by shak­ing the so­lu­tion. The in­di­go carmine is ox­i­dized by the oxy­gen in the air and the col­ors change in the op­po­site di­rec­tion.

Reagents and equip­ment:

  • glu­cose (6 g);
  • in­di­go carmine (0.01 g);
  • 1 M so­lu­tion of sodi­um hy­drox­ide (40 ml);
  • beakers (3);
  • dis­tilled wa­ter.

Step-by-step in­struc­tions

Dis­solve ap­prox­i­mate­ly 6 ml of glu­cose in 200 ml of warm dis­tilled wa­ter, and add 40 ml of sodi­um hy­drox­ide so­lu­tion. In an­oth­er beaker, dis­solve the in­di­go carmine, cre­at­ing a blue so­lu­tion. Then pour the al­ka­line so­lu­tion of glu­cose and the in­di­go carmine so­lu­tion into a large beaker and ob­serve the change in col­or.

Pro­cess­es de­scrip­tion

Ini­tial­ly, the so­lu­tion col­ored by the in­di­go carmine (blue) is ox­i­dized by the oxy­gen in the air to a green col­or – this is the col­or of its ox­i­dized form. When the green so­lu­tion is left to stand, the glu­cose be­gins to re­duce the in­di­go carmine, first to red, and then to yel­low. If you shake the so­lu­tion or de­cant it, it mix­es with air, and the oxy­gen once more ox­i­dizes it to green.

Safe­ty pre­cau­tions

When work­ing with sodi­um hy­drox­ide, wear rub­ber gloves and pro­tec­tive glass­es, as it caus­es burns if it gets on the skin or in the eyes.

Warn­ing! Sub­stances of this ex­per­i­ment are tox­ic and high­ly dan­ger­ous for your health. Do not try this at home. Only un­der pro­fes­sion­al su­per­vi­sion.