Oxidation states of vanadium

The color of the solution changes from yellow to blue, green and purple

Scientific name: Reduction of V(V) to oxidation states II, III and IV

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Safety

Wear eye protection goggles. Work with dry vanadate powder in a hood.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

VO3- + 2H+ → VO2+ + H2O

2VO2+ + SO32- + 2H+ → 2VO2+ + SO42- + H2O

2VO2+ + 2Sn + 8H+ → 2V3+ + 2Sn2+ + 4H2O

2VO2+ + 3Zn + 8H+ → 2V2+ + 3Zn2+ + 4H2O can be represented as three reactions 2VO2+ + Zn + 4H+ → 2VO2+ + Zn2+ + 2H2O

2VO2+ + Zn + 4H+ → 2V3+ + Zn2+ + 2H2O

2V3+ + Zn → 2V2+ + Zn2+

Step-by-step instruction

  1. Prepare a solution of 2M sulfuric acid (75 mL) in a beaker.
  2. Add about 1 gram of ammonium metavanadate.
  3. Stir the resulting mixture until complete dissolution.
  4. Divide the resulting solution into 4 parts, pour it into beakers or tubes.
  5. Prepare a solution of sodium sulfite of random concentration.
  6. Slowly add sodium sulfite to the second beaker until the color changes (it must turn blue)
  7. Fill the third beaker by tin powder (about 10% by volume). Stir vigorously until the color changes to green.
  8. Add zinc powder to the fourth beaker. Vigorously stir the solution. There will be a gradual change in color: yellow-blue-green-purple.
  9. Now you have 4 cups with solutions containing vanadium ions in different oxidation states and having different color
  10. To the fourth glass slowly add a solution of cerium nitrate-ammonium. There will be a gradual change in color: purple-green-blue-yellow.

Scientific background

Vanadium is the only element that may be in four different oxidation states, all of which are stable in aqueous solutions.

Solution becomes yellow due to the presence of ions VO2+.

Sulfite anion is a weak reducing agent that can restore V (V) to a V (IV), giving a solution of a blue color. A stronger reducing agent is tin. It can restore to V (III), giving a solution of a green color.

Finally, most of the proposed strong reductants, zinc, step by step restores V (V) to V (II), giving violet solution.

Ce (IV) - a strong enough oxidizing agent to convert V (II) to V (V).

Danger:
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Difficulty:

Published on 10 March 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst