Chemical Chameleon

Introduction

The Chemical Chameleon is a very interesting and beautiful demo to perform. You start with a purple solution and a colorless one. Once you add them together, you get green then yellow. Not as striking as oscillation reactions (in my opinion) but still a very beautiful demo.

Reagents

• Potassium Permanganate;
• Sodium Hydroxide (Potassium Hydroxide can be used, Ammonia solution should also work);
• Reducing Sugar (Fructose, Glucose, etc.);
• Distilled Water (tap water doesn’t seem to affect the reaction);

Dangers

The demo itself is pretty much safe. Some precautions are needed while preparing the solutions, though.

• Sodium Hydroxide is corrosive. Gloves, while weighting it, are recommended.
• Potassium Permanganate has a bad tendency for staining everything it comes in contact with. However, only a very small quantity of it is going to be used. Stains in your workplace may be cleaned using a solution of Sodium Metabisulfite.
• Glucose and Fructose may cause Hyperglycemia if you add too much into your cavum oris.

Procedure

The procedure for this reaction is quite versatile. Meaning you can do this in a multitude of ways. You may change the quantities used to obtain different timings of the color changes, for instance.

The first step is to prepare the solution of Potassium Permanganate. I added a small pinch (something like 200mg) to about 40mL of water.

Then, prepare a solution of 1g of Sodium Hydroxide and 2g of Fructose (if you are using Glucose use exactly the same quantity).

Finally, add about 10mL of the Permanganate solution to the Sugar/Hydroxide solution and watch!

Note:

Increasing the quantity of Sodium Hydroxide used accelerates the color changes. In the same manner, decreasing it makes the color changes slower.

There are people who prefer to do this reaction in a “reverse” manner. The Permanganate goes into the 250mL of water and the Sugar/Hydroxide goes into the 40mL of water. Adding the 40mL solution to the 250mL one starts the reaction.

Video

I recorded a small demonstration of the reaction. Shaking is optional. Not shacking the reaction vessel can actually make the reaction more beautiful.

Theory

Potassium Permanganate is a strong oxidizer, able to oxidize a Reducing Sugar (Fructose or Glucose, for instance). However, the Permanganate ion gets reduced all the way into Manganese Dioxide (MnO₂) in different steps.

I’ll try to summarize said steps:

• First, Permanganate gets reduced into Hypomanganate, which is blue. This results in a bluish color.

Permanganate, MnO₄^–, Mn⁷⁺ –> Hypomanganate, MnO₄^3-, Mn⁵⁺

• The concentration of Hypomanganate, thus, increases. Now, both Hypomanganate and Permanganate can be reduced. This “allows” the Permanganate to follow another path of reduction, producing green Manganate. The solution turns green.

Permanganate, MnO₄^–, Mn⁷⁺ –> Manganate, MnO₄^2-, Mn⁶⁺

• Finally, the intermediates get reduced all the way to Manganese Dioxide. This produces the yellow color (Manganese Dioxide is actually brown, but the suspension of fine particles of this substance makes the solution light brown/yellow):

Hypomanganate, MnO₄^3-, Mn⁵⁺ –> Manganese Dioxide, MnO₂, Mn²⁺

Manganate, MnO₄^2-, Mn⁶⁺–> Manganese Dioxide, MnO₂, Mn²⁺

The oxidation products of the Reducing Sugar are mainly Glucoronic Acid (if Glucose is used) or Fructonic Acid (if Fructose is used) along with some Arabinonic Acid and even Formic Acid. The Hydroxide used keeps the pH high.

Note: Glucose and Fructose are isomers, having the same atoms, therefore the same molecular weight. That`s why the amount of substance one should use is the same for both of them.

Final Notes

As always, if you have any doubts feel free to comment. Please leave some feedback.