Science Area: Chemistry

Materials:

Thymolphthalein Solution (disappearing ink)

Household ammonia

Clear glass

Water

Spoon

  Safety Considerations:

Perform this experiment under adult supervision (for children).

Keep ammonia and thymolphthalein away from eyes and mouth.

Be careful not to spill the water in the floor.

Use plastic gloves and goggles when handling ammonia.

 Procedures:

Add about 5 table spoons of water in a clear glass.

Add (disappearing ink) to the water  while swirling to mix.

Observe what happens to the disappearing ink.

Add a drop of household ammonia.

Explanation:

The Disappearing Ink is made of thymolphthalein,  and its chemical formula is C₂₈H₃₀O_4.  Thymolphthalein is a water-based acid-base indicator (pH indicator) that changes from a colored when pH greater than 10.5, to a colorless solution when pH less than 9.3.  In other words, acids turn the Disappearing Ink colorless and bases turn it back to blue. Most tap water is slightly acid and it turns the solution colorless. Ammonia is a base and when it is added to the water with  disappearing ink the water turns back blue.

Source:

Product Instructions and pictures

Chemistry Bites. Disappearing Ink. Universe of Science 1998

Information about Thymolphthalein

http://chemistry.about.com/od/chemistryhowtoguide/ht/colorbubble.htm