“Flag in a Test Tube” experiment

How to wake a three-layered mixture

This col­or­ful and vivid ex­per­i­ment demon­strates the prop­er­ties of chromi­um, which in var­i­ous com­pounds, de­pend­ing on the type of ox­i­da­tion, can have prac­ti­cal­ly all the col­ors of the rain­bow.

Reagents and equip­ment:

  • potas­si­um dichro­mate;
  • amyl al­co­hol;
  • sul­fu­ric acid;
  • hy­dro­gen per­ox­ide (10%);
  • test tube.

Step-by-step in­struc­tions

Pour ap­prox­i­mate­ly 15-20 ml of potas­si­um dichro­mate into the test tube, and add 25 ml of amyl al­co­hol. Ob­serve the lay­er­ing of the mix­ture. Then we make our mix­ture acidic with a small amount of sul­fu­ric acid. Then add 1-2 drops of 10% hy­dro­gen per­ox­ide. We ob­serve the re­ac­tion with the re­lease of gas and a change in the col­or of the so­lu­tion. The amyl al­co­hol turns a dark blue col­or, and the space be­tween the lay­ers turns dark-green, al­most black.

Pro­cess­es de­scrip­tion

When amyl al­co­hol is added to a potas­si­um dichro­mate so­lu­tion, the sep­a­ra­tion of the mix­ture takes place. Amyl al­co­hol is a liq­uid that dis­solves poor­ly in wa­ter and has a low­er den­si­ty, so it will float on the sur­face of potas­si­um dichro­mate. Af­ter adding hy­dro­gen per­ox­ide, an in­tense trans­for­ma­tion takes place – the liq­uid be­tween the lay­ers of amyl al­co­hol and potas­si­um dichro­mate turns a dark-green (al­most black) col­or. Oxy­gen is also re­leased. With the in­ter­ac­tion of potas­si­um dichro­mate and hy­dro­gen per­ox­ide in an acidic medi­um, an un­sta­ble com­pound is formed – chromi­um(VI) per­ox­ide, which breaks down al­most im­me­di­ate­ly in the aque­ous so­lu­tion and gives the mid­dle lay­er this dark green col­or. How­ev­er, in or­gan­ic sol­vents such as amyl al­co­hol, chromi­um(VI) per­ox­ide can sta­bi­lize and not break down for con­sid­er­able amount of time. So the up­per lay­er turns blue.

Safe­ty pre­cau­tions

When work­ing with sul­fu­ric acid, wear rub­ber gloves and pro­tec­tive glass­es, as it caus­es burns on con­tact with the eyes and skin. Con­duct the ex­per­i­ment in a fume hood or a well-ven­ti­lat­ed room.

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

Try it