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Redox and Ligand Substitution Chemistry of Cr(II) and Cr(III

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1.What are the Equations?: The redox processes in converting CrO3 to [Cr(H2O)5Br]2+. We dissolve chromium trioxide in acid to get CrO4(2-), and add that to a solution of hydrogen peroxide/perchloric acid. that should give [Cr(H2O)6]3+. This is then passed through a jones reductor into an perchloric acid/bromine solution to give the [Cr(H2O)5Br]2+?
Why does boiling change the colour of the solution (obviously a change in ligands?)

2. Reaction pathway: reduction of [Co(NH3)5Cl]2+ (pink, cobalt(iii)) by [Cr(h2o)6]2+ to give ?? (green solution)
This is then gently heated, and changes colour (to blue) and addition of AgNO3 gives a ppt (AgCl). Why?, and why are the perchlorate salts of cobalt and chromium used?

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Solution Summary

This solution explains:

1) What the redox reactions are for several conversions of chromium (VI) oxide to several chromium complexes.

2) Why color changes occur during redox reactions of several cobalt complexes.

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Redox and Ligand Substitution chemistry of Cr(ii) and Cr(iii)

1.What are the Equations?: the redox processes in converting CrO3 to [Cr(H2O)5Br]2+. We dissolve chromium trioxide in acid to get CrO4(2-), and add that to a solution of hydrogen peroxide/perchloric acid. that should give [Cr(H2O)6]3+. This is then passed through a jones reductor into an perchloric acid/bromine solution to give the [Cr(H2O)5Br]2+?
Why does boiling change the colour of the solution (obviously a change in ligands?)

The first reaction to look at is the change from chromium trioxide to the chromate ion. In both of these forms, the chromium has a +6 charge, so no electrons need to be transferred.

CrO3  CrO4-2

To balance the oxygen, add a water molecule to the left side:

CrO3 + H2O  CrO4-2

To balance the hydrogen atoms, add two H+ ions to the right:

CrO3 + H2O  2 H+ + CrO4-2

Next you need the reaction of chromate ion with the hydrogen peroxide. The ...

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