Chemical Chameleon

Chemistry:	Redox Reactions
Grade Range:	Elementary School, Middle School, High School
Format:	Hands-on, Stage

The Chemical Chameleon is a common demonstration, and is a good introduction to redox reactions. As a hands-on demonstration, students should not directly handle the flask, but can be up close as long as the flask is properly stoppered.

Materials

• 1000 mL Erlenmeyer Flask with Stopper
• 100mL Beaker
• 1000mL Beaker (to Prepare Solutions)
• Bottles with Solutions (See Preparation Below)
  • Potassium Permanganate
  • Sodium Hydroxide
  • Sugar
  • Water

Safety Precautions

Please read the Liquid Chemical section of the Demonstration Safety page before performing this demonstration.

This demonstration requires: safety glasses, disposable gloves. A labcoat is recommended.

Demonstration

Preparation

• Prepare the Potassium Permanganate (KMnO₄) stock solution: In a 1000mL beaker, dissolve 0.5g of KMnO₄ in 500mL of water. Store in a dark bottle with a label and date on it.
• Prepare the Sodium Hydroxide (NaOH) stock solution: for every 500ml of water, dissolve 10g of NaOH in it. Store in a bottle or container with a label and date on it.
• Prepare the Sugar solution: for every 250mL of water, dissolve 6g of sugar. Store in a bottle or container with a label and date on it.

Presentation (Stage)

1. Set out the Erlenmeyer flask and the 100mL beaker. Pour 500mL of the NaOH solution and 250ml of the sugar solution into the flask, and swirl it well to get them mixed.
2. Point to the clear colorless solution, and ask the audience what color you should try to make it. Gather responses from the students, and after several responses let them know that you will try to make it the following colors: Purple, Blue, Green, Yellow, and Red.
3. Show the bottle with the KMnO₄ solution, and measure out 20mL of it with the 100mL beaker. Show that the solution you are adding is purple, and ask the audience for ideas on what will happen when you add it to the flask.
4. Ask for a 3-second countdown. Swirl the flask during the countdown, and at the end pour the KMnO₄ solution in and stopper the flask. Watch as the solution turns blue, then green, and then yellow!
5. Ask the audience if you should try adding more to the solution. If yes, repeat steps 3 and 4.
6. Step 5 can be repeated multiple times. However, be aware that the solution will get darker as you add more of the KMnO₄ solution, and will eventually become too dark to discern a color change. If possible, try to have a light source directly underneath or behind the flask, to ensure that the colors are visible as you add more of the KMnO₄ solution.

Presentation (Hands-on)

1. Set out the Erlenmeyer flask and the 100mL beaker. Pour 500mL of the NaOH solution and 250ml of the sugar solution into the flask, and swirl it well to get them mixed.
2. Once students start to come up, ask them what color they would like to see in the flask: red, yellow, green, blue, or purple. Measure out 20mL of the KMnO₄ solution and ask them what color they think it will turn the flask.
3. Ask for a 3-second countdown. Swirl the flask during the countdown, and at the end pour the KMnO₄ solution in and stopper the flask. Watch as the solution turns blue, then green, and then yellow!
4. For the remainder of the event, add only 10mL of the KMnO₄ solution at a time instead of 20mL. Once your solution becomes too dark to see a color change, it can be safely disposed of by pouring it down a toilet or janitor sink.

Why This Works

Short Explanation

This demonstration works because it is a Redox Reaction. Redox stands for Reduction/Oxidation, which are reactions that happen due to an exchange of electrons. Reduction is when a molecule gains electrons, and Oxidation is when a molecule loses electrons. A helpful way to remember this is with this phrase: "LEO says GER". The letters in LEO stand for Loss Equals Oxidation, and GER stands for Gain Equals Reduction.

When the Potassium Permanganate (KMnO₄) is added into the solution, it is reduced (receives an extra electron) and changes from a purple color to a green color. As this happens, there is a middle period where the colors mix and make the solution look blue. The reduced state then goes through a second slow reduction, which causes a reaction with the water and makes manganese dioxide, a brown-yellow solid, precipitate. In a weak solution, the brown color isn't as apparent, so it will look like it turns yellow! When more of the KMnO₄ is added into the solution and goes through further reductions, the brown color will start to become more prominent, and will make the end solution look like a rusty red instead of yellow.

Full Explanation

COMING SOON

Additional Information

• For an older audience, you can compare the result of this reaction to the color changing medicine from the Mary Poppins movie.
• This demonstration pairs well with the Potassium Permanganate And Glycerin, the Shaking Solution, and the Elephant Toothpaste demonstrations.