Redox and the Goddess of Beauty

Demonstration Kit


A yellow solution containing vanadium(V) ions goes through a series of beautiful color changes as it is swirled and shaken with zinc metal. The final purple solution, which contains vanadium(II) ions, miraculously cycles back through the entire series of color changes when hydrogen peroxide is added.


  • Redox reactions
  • Oxidation states
  • Transition metals


Ammonium metavanadate solution, NH4VO3 in dilute H2SO4, 140 mL*
Hydrogen peroxide, H2O2, 6%, 7 mL*
Zinc, granular, Zn, 5 g*
Erlenmeyer flasks, 500-mL, 2
Graduated cylinder, 250-mL
Magnetic stirrer and stir bar
Pipet, Beral-type
Powder funnel, large
Stopper to fit the Erlenmeyer flask
Weighing dish
*Materials included in kit. 

Safety Precautions

Ammonium metavanadate solution is highly toxic and corrosive to eyes, skin and other tissue. Hydrogen peroxide is corrosive to the skin, eyes and respiratory tract and is a very strong oxidant. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.


Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The ammonium metavanadate solution may be disposed of according to Flinn Suggested Disposal Method #27f. Excess hydrogen peroxide solution may be disposed of by diluting it with water to a concentration of less than 3% and rinsing it down the drain with water according to Flinn Suggested Disposal Method #26b.


  1. Measure 5 g of granular zinc into a weighing dish and transfer the zinc into a 500-mL Erlenmeyer flask using a large powder funnel. Place a magnetic stir bar into the flask.
  2. Using a 250-mL graduated cylinder, measure out 140 mL of the acidic ammonium metavanadate solution. (Observe the initial yellow color of the solution.)
  3. Pour the ammonium metavanadate solution into the Erlenmeyer flask. (The solution will turn green.)
  4. Stopper the flask and begin stirring on the magnetic stirrer to reduce the vanadium (VO2+) ions. (The solution will gradually change color from green to blue to blue-green to dark green to dark blue to purple. The entire sequence of color changes will take about 10–15 minutes.)
  5. After the solution has turned purple, decant the solution into another 500-mL Erlenmeyer flask, leaving the zinc in the first flask. Do not transfer any zinc.
  6. Using a Beral-type pipet, add 6% hydrogen peroxide to the purple solution in 1–2 mL increments, swirling after each addition. (The solution will cycle back through a series of color changes, from purple to blue-green to blue to dark green to brownish red. The entire sequence of color changes will require about 7 mL of H2O2.)
  7. The resulting vanadium solution may be recycled through both the reduction and oxidation sequences to repeat the demonstration. Pour the solution remaining from step 6 back into the flask containing the original zinc, and repeat steps 4–6.

Student Worksheet PDF


Teacher Tips

  • This demonstration has been available for years using zinc (mercury) amalgam as the reducing agent. Given the toxicity and hazard of working with mercury, we retested the procedure using other sources of zinc. We found that granular zinc gives excellent results, as described herein. Use only fresh, high quality, granular zinc. Do NOT use mossy zinc or zinc dust.
  • Dissolving metavanadate ions (VO3) in acidic solution produces VO2+ ions according to the following reaction:

    VO3(aq) + 2H+(aq) → VO2+(aq) + H2O

  • As noted in step 7, both the vanadate solution and the zinc may be recycled to repeat the demonstration. The color changes may take a little longer the second time around, but all of the colors will be observed.
  • The purple solution containing V2+ ions is very stable and will not change color, even after several hours.

Correlation to Next Generation Science Standards (NGSS)

Science & Engineering Practices

Asking questions and defining problems
Planning and carrying out investigations
Analyzing and interpreting data
Engaging in argument from evidence
Obtaining, evaluation, and communicating information

Disciplinary Core Ideas

MS-PS1.B: Chemical Reactions
MS-PS1.A: Structure and Properties of Matter
HS-PS1.A: Structure and Properties of Matter
HS-PS1.B: Chemical Reactions

Crosscutting Concepts

Cause and effect

Performance Expectations

MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

Answers to Questions

  1. Describe what happened in this demonstration.

    A yellow ammonium metavanadate solution was poured into a flask containing zinc. The solution immediately turned green. While swirling the flask, the solution went through a series of color changes, from green to blue to blue-green to dark blue to purple. When the solution was decanted off and hydrogen peroxide was added, the solution went through another set of color changes, from purple to blue-green to blue to dark green to brownish red.

  2. What is an oxidation–reduction reaction?

    An oxidation–reduction (or “redox”) reaction occurs when one or more electrons are transferred between molecules. Oxidation refers to a loss of electrons (and rise in oxidation state), and reduction refers to a gain of electrons (and subsequent decrease in oxidation state).

  3. The initial yellow solution contains VO2+ ions, which include vanadium(V). In the first part of this demonstration, vanadium(V) was reduced stepwise by zinc to vanadium(IV), then vanadium(III), and then vanadium(II). Write a balanced chemical equation for the each of the steps in this reaction. Hint: Include hydrogen ions in the first two reactions.
    1. V(V) to V(IV)

      Zn(s) + 2VO2+(aq) + 4H+(aq) → 2VO2+(aq) + Zn2+(aq) + 2H2O(l)

    2. V(IV) to V(III)

      Zn(s) + 2VO2+(aq) + 4H+(aq) → 2V3+(aq) + Zn2+(aq) + 2H2O(l)

    3. V(III) to V(II)

      Zn(s) + 2V3+(aq) → 2V2+(aq) + Zn2+(aq)

  4. VO2+ ions are yellow, while VO2+ ions are blue. Knowing this, explain the green color that was generated when the ammonium metavanadate solution was poured over the zinc.

    The green was an intermediate color, due to the combination of yellow VO2+ ions from the ammonium metavanadate solution and blue VO2+ ions that the zinc was already producing.


The initial yellow ammonium metavanadate solution contains VO2+ ions and illustrates vanadium in the +5 oxidation state, vanadium(V). The yellow vanadium(V) is reduced stepwise by zinc through the following oxidation states—vanadium(IV) in VO2+ (blue), vanadium(III) in V3+ (blue-green), and finally vanadium(II) in V2+ (purple). The balanced equations for the stepwise reduction of vanadium by zinc are shown.

Reduction of vanadium by zinc:

The intermediate green color observed when the yellow solution is initially poured into the flask containing zinc is due to the combination of the yellow VO2+ and the blue VO2+ ions.

Vanadium in the +2 oxidation state, V2+, is reoxidized using hydrogen peroxide. The various oxidation states are observed by the gradual addition of hydrogen peroxide. In a strongly acidic solution, hydrogen peroxide will convert the vanadium all the way to the red-brown peroxovanadium cation, VO23+, in which vanadium in the (+5) oxidation state is combined with the peroxide anion, O22–.

Oxidation of vanadium by hydrogen peroxide:
Vanadium, element 23, was named after Vanadis, the Norse goddess of beauty, because of its beautiful, multicolored compounds. The principal oxidation state of vanadium is +5, which is found in compounds such as the orange vanadium(V) oxide, V2O5, an industrial catalyst. In aqueous solution, vanadium can exist in many different oxidation states, from +5 to +2. Each oxidation state has a different representative color. Many transition metal ions form complexes to give a rainbow of colors. The colors arise because transition metal ions have incompletely filled d subshells. The d electrons can be excited from a lower energy state to a higher energy state by absorbing light of the appropriate wavelength and energy.


Davis, J. M. J. Chem. Educ. 1968, 45, 473.

Grant, A. W. J. Chem. Educ. 1977, 54, 500.

Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements Pergamon Press, 1984, 1157.

Hentz, F. C.; Long, G. G. J. Chem. Educ. 1978, 55, 55.

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