Vanadium Oxidation States
Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★☆ Some safety precautions required to perform safely
Categories: Colour Changes, Elements and Periodic Table, Oxidation and Reduction
Alternative titles: Colors of Vanadium
Summary
This experiment demonstrates the multiple oxidation states of vanadium by producing vivid colors (yellow, green, blue, dark-green, and purple) in a single solution. Starting from vanadium pentoxide, vanadium compounds are reduced with zinc and then re-oxidized with potassium permanganate, creating a reversible rainbow of colors.
Procedure
- Prepare sodium vanadate by heating vanadium pentoxide and sodium carbonate in water until the solution turns green.
- Add concentrated sulfuric acid to the sodium vanadate solution to form yellow vanadyl sulfate (V⁵⁺ state).
- Transfer the solution to a flask and heat gently while adding zinc granules.
- Observe as the solution changes colors: yellow (V⁵⁺), green (V⁴⁺), blue (V³⁺), dark-green, and finally purple (V²⁺).
- Pour samples into separate beakers at each stage to preserve the different colors.
- To reverse the sequence, add potassium permanganate to re-oxidize the solution, changing the colors back through green, blue, and yellow, then to orange and red.
Links
Oxidation States of Vanadium - Rugby School Chemistry:
📄 Vanadium Oxidation States Experiment - ChemTalk: https://chemistrytalk.org/vanadium-oxidation-states-experiment/
Variations
- Explore the stability of each color by leaving the solutions exposed to air for different amounts of time.
Safety Precautions
- Wear safety goggles, gloves, and a lab coat at all times.
- Vanadium compounds are toxic—avoid inhaling dust or vapors and prevent skin contact.
- Handle sulfuric acid with care; it is highly corrosive.
- Potassium permanganate is a strong oxidizer—do not mix with flammable or organic materials.
- Work in a well-ventilated area or fume hood when handling powdered chemicals.
- Dispose of vanadium compounds properly as heavy metal waste; do not pour large amounts down the drain.
Questions to Consider
- Why do vanadium compounds display so many different colors? (Because d-orbital electrons absorb light at different wavelengths depending on the oxidation state.)
- Why is zinc used in this experiment? (It acts as a reducing agent, lowering the oxidation state of vanadium step by step.)
- Why does the purple V²⁺ state fade quickly in air? (It is unstable and gets oxidized back to V³⁺ by oxygen.)
- What is the role of potassium permanganate? (It is a strong oxidizing agent that reverses the reduction and restores higher oxidation states of vanadium.)