The term goldenrod is typically used to describe a color of paper – golden yellow. Certain brands of goldenrod paper contain a special dye that turns bright red in solutions that are basic like ammonia water or washing soda. The paper turns back yellow with an acid like vinegar or lemon juice.
1. Place a piece of goldenrod paper on the table. Make sure that table is clean and the work surface is dry.
2. Place a drop of water on one of the corners of the paper. Does anything happen?
3. Fill a jar with a small amount of ammonia water. Dip a cotton ball in the ammonia water and wipe it across the top portion of the goldenrod paper. Save the bottom half of the paper for step 5. Does anything happen?
4. As you continue to wipe designs on the goldenrod paper, notice that the paper does not stay red forever. What is causing the paper to change back to yellow?
5. Use the old piece of wax candle to write a secret message (such as “Hi!” or “WOW”) across the bottom half of the paper.
6. Wipe the cotton ball with ammonia water across the secret message to see what develops.
How does it work?
The ammonia on the cotton ball is a base and causes the dye in the special goldenrod paper to change color. You probably noticed that the red color fades over time and the paper eventually changes back to its original yellow color. Why? The carbon dioxide gas that is in the air we breathe is slightly on the acidic side of the pH scale. The carbon dioxide reacts with the ammonia on the paper to produce ammonium carbonate, which changes the pH of the paper to neutral (roughly a pH of 7) and the dye changes back yellow. If you use a stronger base like washing soda, the red message will become not disappear with just the carbon dioxide in the air. You will need to use a stronger acid like lemon juice or vinegar to change it from red to yellow. You can also use goldenrod paper as inexpensive pH paper to classify safe household products as being either acidic or basic.
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