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

Caption: Chromate ion equilibrium experiment. The beaker contains yellow potassium chromate (VI) solution. This contains the chromate (CrO4 2-) ion, in equilibrium with the orange dichromate (Cr2O7 2- )ion. The equilibrium is heavily towards the chromate side in alkali conditions. When sulphuric acid is added, the equilibrium shifts to the dichromate side, changing the colour of the solution to orange. 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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