Milk of magnesia, a suspension of magnesium hydroxide, is mixed with a universal indicator to show its alkaline nature. When vinegar is added, the solution rapidly shifts through the color spectrum as the acid reacts with the base, demonstrating how antacids neutralize stomach acid.

1. Pour about 100 mL of milk of magnesia into a 500 mL beaker and dilute with tap water until the beaker is half full.
2. Add 10 mL of universal indicator. The solution should appear light blue, indicating slight alkalinity.
3. Stir continuously (using a magnetic stirrer or by hand).
4. Add 10–20 mL of vinegar or 1M hydrochloric acid and observe the color change to red as acidity dominates.
5. Watch as more magnesium hydroxide dissolves, neutralizing the acid and shifting the color back through orange, yellow, green, and blue.
6. Continue adding vinegar in small amounts to repeatedly demonstrate the full color spectrum shift.

Milk of Magnesia: A Colorful Chemistry Demonstration - Chemical Kim Science:

Magic Rainbow - Fun Chemistry Experiment with Milk of Magnesia and Vinegar - Beals Science:

📄 Color Changing Milk of Magnesia - Steve Spangler: https://stevespangler.com/experiments/color-changing-milk-of-magnesia/

• Use red cabbage juice instead of universal indicator for a natural pH color change.
• Perform the demonstration in a large clear container for a classroom show effect.

• Safety glasses required.
• Handle glassware carefully to avoid spills and breakage.
• Do not ingest the experimental mixture.
• Dispose of the solution safely by diluting with plenty of water down the sink.

• Why does the solution initially appear blue before vinegar is added?
• What chemical reaction is taking place between magnesium hydroxide and acetic acid (vinegar)?
• Why does the solution change color multiple times as the reaction continues?
• How does this experiment model what happens when people take antacids for heartburn?