Traffic Light Reaction

Source

• Chemical Demonstrations: A Sourcebook for Teachers, Summerlin and Ealy, page 111
• Chemical Demonstrations: A Handbook for Teachers of Chemistry, Shakhashiri, Volume 2, page 142

Scaling Up

• Scale the procedure from 250 mL to 2 L for a lecture demonstration.

Chemicals

Chemical	Amount
Glucose	3.0 g
Sodium Hydroxide (NaOH)	5.0 g
Indigo Carmine	2.0 g

Solutions Preparation

1. Glucose/NaOH Solution:

• Combine 3.0 g glucose and 5.0 g NaOH in 0.250 L of water. Mix well.

1. Indigo Carmine Solution:

• In a separate container, add 2.0 g of indigo carmine to 200 mL of water. Mix thoroughly.
• Note: Make this solution fresh!

Procedure

Initial Setup:

• Place 50 mL of the glucose/NaOH solution in a 250 mL flask.
• Add 5-10 mL of the indigo carmine indicator solution. The solution should start out as light yellow (the indicator is reduced by alkaline dextrose, producing yellow).

Stopper and Swirl:

• Stopper the flask and gently swirl it.
• The solution should turn red as swirling introduces oxygen, which oxidizes the indicator and produces the red color.
• If the red color does not persist, add more indicator.

Shaking the Flask:

• Shake the flask. This introduces more oxygen and causes further oxidation of the indicator, resulting in a green color.

Observation:

• Allow the solution to stand. The dextrose will reduce the indicator back to the yellow color.

Safety Precautions

• Wear appropriate personal protective equipment (PPE) including gloves and goggles.
• Handle sodium hydroxide with care, as it is caustic.

This demonstration effectively illustrates the principles of oxidation and reduction through a visually engaging traffic light reaction.