Cody Svoboda

Colored Bottle

Science Concept: A variety of indicators will be affected by the reaction with the oxygen present in the air.

Materials:

• 500 mL round bottom Florence flask with rubber stopper with no holes
• 20 g. of Potassium hydroxide dissolved in 1 L. of water
• 10 g. of Glucose
• Spatula tip of Indophenol indicator (very small amount)

  *This will stain your hands and clothes

• 5 drops of Resazurin

Preparation:

Pour the 250 mL of Potassium hydroxide solution in to he flask. Then add the 10 g glucose, the indophenol indicator, and the resazurin. Wait for the solution to turn colorless. This may take about 10 minutes.

Demonstration: Shake the flask with your thumb on the stopper. Shake the flask and the solution should turn from colorless to a pink color. Shake the flask again and the solution will turn from pink to purple. Shake the flask the third time and the solution will turn from purple to blue. If the flask is left standing it will turn pink, and then colorless again. The shaking can be repeated numerous times.

Introduction: Most of the other students are doing reactions by adding 2 solutions, but I am not going to add anything. Can anyone tell me what color the solution is in my bottle? (Shake it). I am going to have to ask again because you guys must have not gotten a close enough look. My solution is pink. Now tell me again, what color my solution is. (Shake it). Are you guys able to see the solution clearly, because I see it as purple? I'm going to ask once more, what color is this solution? What do you think is going on with the solution in my flask?

Explanation: Even though it didn't look like I added anything to cause this reaction, when I shook the bottle I actually did. Can anyone guess what it was?? (Yes, Oxygen or Air). The flask contains the indicators indophenol and resazurin. When the indicators react with the oxygen inside the flask, it turns the solution different shades of red and blue. The indicators combine with the oxygen in the form of a redox reaction. The first shake of the solution turns pink, and with two more shakes the color deepens to a blue shade because more oxygen is allowed to react with the indicators. If the solution is allowed to stand, the oxygen in the solution is gradually used up by the glucose and it will return back to colorless. The flask can be used repeatedly for 2 hours.

Safety:
Always use a rubber stopper without a hole so you don't have to worry about any of the solution escaping from the flask. Shake the flask with your thumb on the stopper.
Always wear goggles in case the solution does spray from the flask.
The Potassium hydroxide is a strong base. Do not get any on your hands or anywhere near your eyes.
Wear plastic gloves while handling the Indophenol indicator. This will stain your hands and clothes if you get it on them.

Waste Disposal: This solution can be put down the drain with no risk of any damage or danger to the sink or yourself.

Reference: Chen, Philip S,Entertaining and Educational Chemical Demonstrations, Chemical Elements Publishing Co, 1974, p. 37-40.

Other examples based upon the same prinicples can be found in:

Vandaveer, Walter R. IV; Mosher, Mel. The Blue Bottle Revisited J.
Chem. Educ. 1997 74 402.