What does this have to do with Erin Brockovich?


Molecular Structure of Chromate  

Molecular Structure of Dichromate


The molecular structures above show the two common polyatomic oxyanions of chromium (VI).

Name the molecular shape of the chromate ion ______________ . Note: You can change the axis of rotation of the image by left-clicking on the image, and remember that you can turn off the rotation by right-clicking on the image.

Look at the angle formed by the central oxygen in dichromate.  Explain why this angle is formed.

Write the formulas for chromate  ____________  and dichromate ________________.

a solution of chromate 

a solution of dichromate



  Observed:  Dichromate forms under two conditions:

      1)   High concentrations of chromate                 2)   Acidic conditions

 according to the equation

2 CrO42- (aq) + 2 H3O +(aq)            Cr2O72- (aq) + 3H2O (l)

Look at the molecular structures of the reactants, and visualize the exchange that produces the dimer dichromate and water:


                              In the dimerization process, a kind of dehydration synthesis, each hydronium ion contributes

 a  ______________, and one of the chromate ions contributes an ______________ to make a

____________ molecule and dichromate. 


   Question:  What happens when conditions are acidic, but chromate concentrations are low?


    Write the formula for bichromate, the Cr(VI) oxyanion that is formed under these conditions _____________.  

   Write the balanced equation for the formation of bichromate from low concentrations of chromate under acidic conditions:


Created by: Melanie Rock         Montgomery Blair High School         6/2003

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