Objectives

To demonstrate how goldenrod paper can be used as an acid/base indicator

Materials

• Goldenrod paper* (generally found at science supply store)
• Vinegar or lemon juice
• Ammonia (ie Windex®)
• Cotton swab

Procedure

Spray your hand with Windex®. Then slap it on the paper. What happens?

Conclusion

The ammonia on your hand (from the window cleaner) is a base and causes the dye in the special goldenrod paper to change to red. As a result, when you touch the paper, it changes to red! For an immediate change from red back to yellow, vinegar, an acid is used. You can use a cotton swab to “paint” the hand mark. Even without using the vinegar, the red color will fade over time, and the paper will change back to its original yellow color. This is because carbon dioxide in the air, which is slightly acidic, reacts with the ammonia on the paper to produce ammonium carbonate. This changes the pH of the paper to neutral, thus changing the dye on the paper back to yellow.