Return to Lecture Demos page

Ammonia Fountain Why is water drawn up into the flask?

This picture shows the apparatus used in this demonstration. There is a beaker of water below and an inverted flask containing ammonia gas, NH3.

The beaker of water and the flask of ammonia are connected by a glass tube that extends down into the water and up through the rubber stopper into the flask of ammonia. In this picture the end of the tube in the water is sealed with a small pipet bulb.

There is a second tube that extends through the rubber stopper that has a small pipet bulb filled with water.

Click on the small pictures to view the video. The file will open in a new browser window.

Video for Windows

Quicktime

First, the small pipet bulb which seals the glass tube in the water is removed. Then, the small pipet bulb that is filled with water is squeezed so that the water it contains is pumped into the flask of ammonia gas.

When water in the pipet bulb is squeezed into the ammonia gas, NH3 dissolves in the water. NH3(g) + H2O(l) ----> NH4OH(aq)

When NH₃ dissolves in the small amount of water squirted into the flask, it creates a vacuum which pulls water from the beaker below up the tube and into the flask of gas. More NH₃ dissolves, which pulls more water from below. This creates a fountain effect. The pink color comes from phenolphthalein indicator in the water which is colorless until OH^- ions are formed.