Oxygen States of Vanadium
Materials
1 liter Florence Flask with rubber stopper
Zink Amalgam
Bottle of Acidic Ammonium Vanadate Solution
Magnetic Stirplate
600 mL beaker with a stirbar
Rinse Bottle with Cerium Sulfate Solution
Gloves and Goggles
Procedure
Before class starts, place 50gm Zn amalgam in a 1 liter Florence flask. To perform this demo, add 200ml acidic ammonium vanadate solution to the Florence Flask. The solution will turn from yellow to green on contact with zinc amalgam. Stopper the Flask. Then swirling the Flask turns the solution blue, and shaking the flask will turn the solution violet. Then decant the solution into a beaker with a stirring bar. Using cerium sulfate solution, titrate purple solution on a stirring plate.
Approximate amounts of CeSO4 to add to 50ml of V2+ violet solution:
ml CeSO4 added | color of V soln |
20ml | violet to blue |
35ml | blue to green |
40ml | green to yellow |
Reactions
[yellow to green] Zn(s) + VO3- + 8 H3O+ (aq) --> VO++ (aq) + Zn2+ (aq) + 12H2O
[green to blue] Zn(s) + VO2+ (aq) + 4H3O+ (aq) --> 2V3+ (aq) + Zn2+ (aq) + 6H2O
[blue to violet] Zn(s) + 2V3+ (aq) --> 2V2+ (aq) + Zn2+ (aq)
[violet to blue] Ce4+ (aq) + V2+ (aq) --> V3+ (aq) + Ce3+ (aq)
[blue to green] Ce4+ (aq) + V3+ (aq) + 3H2O --> VO2+ (aq) + Ce3+ (aq) + 2H3O+ (aq)
[green to yellow] Ce4+ (aq) + VO2+ (aq) + 6H2O --> VO3- (aq) + Ce3+ (aq) + 4H3O+ (aq)