The Chemistry of Chromium (Demo)
- Page ID
- 3058
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Chemical Concepts Demonstrated
- Cr2+, Cr 3+, and Cr (IV) oxidation states of chromium
Demonstration
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Observations and Explanations
Dish | Observation / Explanation |
---|---|
A + B | Violet solution of Cr(H2O)6 3+. |
C | The color of the solution changes from violet to an "acid green". |
D | Green Cr(OH)3 precipitates from the green solution. More base will cause the solid to redissolve to give a green chromite Cr(OH)4 -solution. |
E | The green solution changes to orange as the CrO42-/Cr2O72- ions are formed. |
E + HCl | After the HCl is added a series of erratic color changes are observed. When the reaction is complete the solution is green. |
A, C, & D with HCl | Solution A remains violet. Solution C changes from green back to violet. Solution D produces another green solution. |
B with HCl & Zn | When the solution becomes acidic, several pieces of Zn are added to the dish. The bright blue color of Cr2+ (aq) will be visible momentarily, but air oxidation rapidly converts this to a green solution. |
Original solution + BaCl2 + Pb(NO3)2 | A yellow precipitate of BaCrO4 will form. Adding HCl will redissolve the precipitate and produce an orange-yellow solution. Pb(NO3)2 produces another yellow precipitate, PbCrO4. |