Shaking Solution

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

This is a common demonstration for Reduction/Oxidation reactions. It is easy to prepare, easy to perform, and after preparation it can be used for several hours!

Materials

• Sodium Hydroxide
• Dextrose (Sugar)
• Water
• 500 mL Erlenmeyer flask
• Stopper for flask
• Indicator: Methylene Blue or Resazurin

Safety Precautions

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

During preparation, wear safety goggles and gloves. During the presentation, make sure whomever is shaking the solution keeps a hand on the stopper, to prevent it from coming out.

Demonstration

Preparation:

1. In the Erlenmeyer flask, combine 300 mL of water with 8g of Sodium Hydroxide and 10g of Dextrose. Add the solids individually, and allow the first to dissolve fully before adding the next one.
2. If your indicator is not already in a water solution, then combine 0.5-1.0 g of the indicator with 50mL of water. Stir thoroughly, store in a bottle and label it. Add 8-10 drops of the indicator solution to the Erlenmeyer flask, and then stopper the flask.
3. The solution will initially be blue (Methylene blue) or purple/pink (Resazurin). After you let it sit, the solution will turn clear (Methylene) or light teal (Resazurin), and it is now ready to use.

Presentation:

1. Show the solution to the students, and swirl the bottle gently. A very slight color change will happen. Let it sit, and after a few seconds the color will disappear!
2. Ask a student to hold it and shake it. The solution will now turn colors dramatically! the more they shake it, the more pronounced the color will become, and the longer it will take for the color to dissipate.
3. Ask the students why it changes colors. What is happening when we shake it? Is there more than one thing going on here?

Why This Works

This demonstration works because it is a Redox Reaction. Redox stands for Reduction/Oxidation, two types of reactions that, typically, involve an exchange of electron charges, usually by use of Oxygen atoms. Reduction is when a molecule loses an Oxygen, and gains electrons. Oxidation is when a molecule gains an Oxygen, and 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.

Remember: There is air all around us, including inside of the flask, and part of that air is Oxygen. So when the flask is shaken, some of that Oxygen dissolves into the solution. It bonds to the dextrose, which causes it to be oxidized. The indicator can tell when glucose is oxidized, and when that happens the indicator changes color.

Full Explanation

Redox stands for Reduction/Oxidation. Reduction is when electrons are gained, usually by the loss of an Oxygen. Oxidation is when electrons are loss, usually by the gain of an Oxygen. 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.

In this experiment, we are seeing a color change when the oxidation of Methylene Blue takes place.

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Additional Information

• Redox Reactions are all around us! Combustion is a redox reaction, and rust on metals is one as well!
• Methylene Blue is used to check the quality of milk produced. After added to some milk, the rate that it turns blue determines what rating the milk gets. A slow change is good, and a fast change is poor.
• This demonstration is a part of the Chemistry Show!