Credit: UNIVERSITY OF NOTTINGHAM/MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY

Caption: Chromate ion equilibrium experiment. The beaker contains orange potassium dichromate (VI) solution. This contains the dichromate (Cr2O7 2-) ion, in equilibrium with the yellow chromate (CrO4 2- )ion. The equilibrium is heavily towards the dichromate side in acidic conditions. When alkali sodium hydroxide is added, the equilibrium shifts to the chromate side, changing the colour of the solution to yellow. This change in the equilibrium position occurs because the chromate ion side of the equilibrium also contains two free acidic protons (H+), whose existence is favoured under alkali conditions. This is an example of Le Chatelier's principle. The full equilibrium equation is: Cr04 2- + 2H+ <---> Cr2O7 2- + H2O. See clip K002 9074 for the full demonstration.

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Keywords: 6+, a level, a-level, adding, beaker, changing, chemical, chemicals, chemistry, chromate, chromium 6, chromium vi, colour change, colours, demonstrating, demonstration, dichromate, education, equilibria, equilibrium, experiment, footage, glassware, lab, laboratory, le chatelier's principle, orange, potassium, pouring, school, science, solution, solutions, technician, yellow

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Chromate ion equilibrium experiment

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