The Pink Catalyst
Publication No. 12537
Add a pink cobalt chloride solution to a colorless solution containing potassium sodium tartrate and hydrogen peroxide and watch as a very obvious green-colored complex forms. As the reaction ends, the solution will return to its original pink color—mindicating that the cobalt chloride catalyst is not used up in the reaction.
(for each demonstration)
Cobalt chloride solution, CoCl2•6H2O, 0.1 M, 12 mL*
Hydrogen peroxide solution, 6%, H2O2, 40 mL*
Potassium sodium tartrate solution, 0.21 M, 100 mL*
Graduated cylinders, 25- and 100-mL
*Materials included in kit.
Cobalt(ous) chloride is toxic by ingestion (LD50 766 mg/kg) and causes blood damage. Hydrogen peroxide is an oxidizer and a skin and eye irritant. Although potassium sodium tartrate solution is considered non-hazardous, do not ingest the material. Avoid body tissue contact with all chemicals. Wear chemical-resistant goggles, chemical-resistant gloves and a chemical resistant apron.
Dispose of the final solution according to Flinn Suggested Disposal Method #27d. Consult your current Flinn Scientific Catalog/Reference Manual for proper disposal procedures.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAnalyzing and interpreting data
Constructing explanations and designing solutions
Disciplinary Core IdeasMS-PS1.A: Structure and Properties of Matter
MS-PS1.B: Chemical Reactions
HS-PS1.B: Chemical Reactions
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.
The solution starts out pink due to the pink color of the cobalt chloride catalyst. The solution turns green forming an intermediate between the catalyst and potassium sodium tartrate. The solution returns to the original pink color of the cobalt chloride solution demonstrating and confirming the fact that a catalyst does not get used up in a chemical reaction.
On the action of hydrogen peroxide, the cobalt(II)–tartrate complex becomes oxidized to a green, probably binuclear, Co(III)–tartrate compound. This cobalt(III)–tartrate is reduced both by tartaric acid and hydrogen peroxide to Co(II)–tartrate with a concomitant evolution of CO2 and O2, respectively. Since the color of the solution is green throughout the reaction, and most of the cobalt is present as Co(III), then the first step (oxidation) is most likely faster than the reduction of Co(III)–complex. (Toth, 1980).
This demonstration also allows you to demonstrate kinetics—the effect of temperature on the rate of a chemical reaction. For each 10 °C increase in temperature, the reaction rate will approximately double. The reaction may be timed at various temperatures. Suggested temperatures and their corresponding reaction times are:
50 °C—200 seconds; 60 °C—90 seconds; 70 °C—40 seconds
Deroo, Julius, Sci Teach., 1974, 41, 44.