When a few drops of water are added to ammonia gas in an inverted florence flask, the vacuum is filled with water and the water changes color The Ammonia Fountain

Purpose  To see what happens when ammonia gas reacts with a small amount of water  To observe the color change of litmus  To demonstrate how a partial vacuum is formed and filled

Demonstration  Ammonia gas was in the florence flask  When a few drops of water were added to the flask, the ammonia completely reacted with the water  A partial vacuum was produced in the flask  Water with indicator rushed from the beaker into the flask and changed to purple

Concepts 1.Equilibrium Reaction 2.Partial Vacuum 3.Indicators

1.Equilibrium Reaction  Ammonia gas reacts with water NH 3 (g) + H 2 O(l) NH 4 + (aq) + OH - (aq)  When ammonia reacts with water there are four “species” formed since this is an equilibrium reaction  Hydroxide ion makes the water “basic” ammoniaammonium ion water hydroxide ion

2.Bases  A base is defined as a substance that produces hydroxide ion when dissolved in water  Ammonia produces hydroxide ion in water  Ammonia is therefore a base

3.Indicators  Indicators are substances which change color in acids or bases  Litmus is a common indicator  Litmus is orange in acid when in water but purple in bases

Conclusions  The gas in the florence flask filled it completely, but all the gas dissolved and reacted in just a few drops of water  When the gas reacted in the water, water rushed in to fill the space it originally occupied

Comments (I)  There are many classic fountain demonstrations commonly performed  Instead of ammonia, hydrogen chloride or other water-soluble gas could be used

Comments (II)  A base is a substance that produces hydroxide ions when dissolved in water  A acid may be thought of as the opposite of a base: an acid produces hydrogen ions when dissolved in water  Hydroxide ions will react with hydrogen ions to produce water OH - + H + H 2 O