Chemistry: Demo: The Ammonia Fountain

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This is one of my favorite demos. This is the ammonia fountain. What I have here is a flask that has ammonium hydroxide in it. What I'm going to do is I'm going to heat the ammonium hydroxide such that it starts to boil. Now when the ammonium hydroxide boils, the ammonia is going to be released. Ammonium hydroxide is a solution of ammonia dissolved in water. And when it boils, the ammonia gets released as a gas and fills the inside of this flask. After this happens, I'll smell the ammonia and I'll know that the flask is full of ammonia. I'll take the ammonia off of the Bunsen burner, and let it cool a little bit. Then I'm going to stick the tip of this tube here inside the water. What's going to happen is the ammonia gas is going to dissolve just where the tip of the tube dissolves in water, because ammonia gas is soluble in water, and this water is now cold. It's not boiling. It's not releasing all of the ammonia. And as soon as a little bit of ammonia dissolves in the water, that's going to create a partial vacuum, because now there are fewer molecules of ammonia that are filling up this tube. The pressure on the outside of the water here is going to push the water up inside this flask, and we're going to get the ammonia fountain.
So let's go ahead and light the Bunsen burner and do the demo. The first thing you have to do to light a Bunsen burner is have the gas going. The second thing you do is you light it. Now here's a Bunsen burner, here's ammonium hydroxide solution inside the flask here. I'm going to heat it to where it starts boiling. You can see the water boiling, and you can hear it abgassing. Now I'm going to let it cool. And when it stops abgassing, I can definitely smell the ammonia. The other important thing to remember when doing this demo is to make sure the stopper is on good and tight.
Now you can see the water rising up as the ammonia dissolves at the interface. There it goes, just like that. Pretty soon it's going to come all of the way to the top and it's going to fill the flask. You'll notice it starts off slow. Then it takes off. Now you notice it's turning pink, pink-red. The reason it's getting pink is because I put some phenalthalline indicator inside the water hear. And as soon as the phenylthalline comes up, I put a little sodium hydroxide inside the solution here as well. And now it turns the color of pink, which is the color of base when it reacts with phenylthalline. Phenylthalline is an acid-base indicator.
So the water is going to come up and fill the flask as much as the ammonia gas was inside the flask. And again, the water is coming up to fill the vacuum that was created by the ammonia gas dissolving inside the water. And the ammonia gas was formed when we boiled the ammonium hydroxide, because the ammonia is going to be less soluble in boiling water than it will be in water at room temperature.
This keeps going. So there you have the ammonia fountain.
Gases
The Ideal Gas Law and Kinetic-Molecular Theory of Gases
CIA Demonstration: Ammonia Fountain Page [1 of 1]