5.2.5 CIA Demonstration: The Ammonia Fountain

Question 1

CIA Demonstration: The Ammonia Fountain

Answer 1

• Ammonia is less soluble in boiling water than in water at room temperature.
• This property is used to create a partial vacuum in a flask, which allows water to be pushed up a tube, creating a fountain effect.

Question 2

note

Answer 2

• A flask containing aqueous ammonia is heated. Ammonia is less soluble in boiling water than in water at room temperature. This property causes the flask to be filled with ammonia gas.
• The flask is then inverted with a tube running into a beaker of water at room temperature. Some of the ammonia dissolves in the water, creating a partial vacuum inside the flask. Since the pressure is lower inside the flask than it is outside the flask, water is drawn into the flask.
• Phenolphthalein is a pH indicator that changes from clear to pink in basic solution. When the ammonia reacts with the water, ammonium ions and hydroxide ions are produced. Hydroxide ions make the solution basic, and the phenolphthalein turns pink.