Reduction of Potassium Bichromate by zinc at acidic media

The color of the solution changes from yellow to green and blue

Scientific name: Reduction of Potassium Bichromate by atomic hydrogen


Acidified Dichromate and Zinc

Восстановление бихромата калия атомарным водородом.

Exothermic reaction. Nitric acid, potassium chromate and zinc

by Marc


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Reaction formula

3 Zn + K2Cr2O7 + 14 HCl → 3 ZnCl2 + 2 CrCl3 + 7 H2O + 2 KCl

Zn + 2 HCl → ZnCl2 + 2 H (in situ)

Step-by-step instruction

  1. Pour 10 ml of hydrochloric acid 2M into a test tube.
  2. Dissolve a small amount of potassium dichromate in the same test tube.
  3. Add a few pieces of zinc.
  4. Observe the formation of gas bubbles and the change in color: yellow - green - blue.

Scientific background

The interaction of zinc with acid generated atomic hydrogen which has not yet bonded into a molecule. Atomic hydrogen is a very strong reducing agent and recovers Cr(VI) to Cr(III) and Cr(II).


Published on 30 April 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst