Ammonia fountain

Water absorbs ammonia and fills the flask

Difficulty:
Danger:
Duration:
15 minutes
Experiment's video preview

Reagents

Safety

  • Put protective gloves on.

  • Conduct the experiment on the tray.

General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

Fountain did not work. What is wrong?

Fountain might have failed due to various reasons:

  1. The flask, which you filled with ammonia, should have been dry. The fountain might have failed if the flask was wet inside before you started or if it was filled with significant amount of water vapor during the experiment. Thoroughly rinse the flask with water to dissolve and wash out all the ammonia residue. Pour the solution down the drain. Dry the flask – with a hair dryer, for instance – and repeat the experiment.

  2. Plastic tubes might have been loosely inserted into the stopper, letting air permeate into the flask. Make sure that the tubes fit in the stopper well.

  3. There might have not been enough liquid in the end of the tube. Take the rubber stopper out and fill the flask with ammonia again. Dip the sharpened end of the tube in the thymol blue solution (make sure some liquid remains in the end of the tube). Then, finish the experiment according to the experiment card instructions.

  4. The stopper might have not been sealing the flask securely. It is crucial to close the flask tightly! Be sure to hold it with your finger.

Step-by-step instructions

Step-by-step instructions
  1. Pour out all the calcium oxide from the bottle into an empty test tube. To shake the powder out, insert the bottleneck into the test tube and tap them on the table.
  2. Using the same trick, pour out all the ammonia chloride NH4Cl from the bottle (1 g) into the same test tube.
  3. Insert the test tube into a beaker. Add 0.5 mL of water into the test tube.
  4. Cover the test tube with a flask to collect the releasing gas. Wait for about 5 min., until the mixture stops bubbling.
  5. Take a disposable plastic cup and add in there 10 drops of 2M sodium bisulfate NaHSO4 solution and 10 drops of 0.01M thymol blue solution.
  6. Top the cup with water.
  7. Insert the tubes into the rubber stopper, as shown.
  8. Dip the thin end of the tube into solution in the plastic cup.
  9. Quickly and securely insert the rubber stopper into the flask.
  10. Immerse the tube in the solution in the plastic cup and wait 2 min.
  11. Liquid will come up into the flask in form of a blue fountain.
  12. Fill up the tube with water to dispose.

Graphical step-by-step instruction

Expected result

Being collected in a flask, ammonia dissolves in water. The pressure inside the flask drops, and the liquid rushes up into it. This is how the fountain works!

Disposal

Fill the tube with mixed substances halfway with water. Close the tube securely. Dispose of the experiment residues along with regular household trash.

Scientific description

How is ammonia formed?

When we add water to the test tube with calcium oxide CaO and ammonium chloride NH4Cl, the following reactions take place:

CaO + H2O → Ca(OH)2

Ca(OH)2 + 2NH4Cl → CaCl2 + 2NH3 + H2O

Calcium oxide reacts with water to form calcium hydroxide Ca(OH)2. This process is exothermic, which means a lot of heat is released during it. At the same time, calcium hydroxide reacts with ammonium chloride, giving ammonia. The heat from the first reaction makes ammonia actively evolve into the flask, by which the test tube is covered.

Why does water start flowing into the flask?

Ammonia NH3 is highly soluble in water. And thus, some of the ammonia from the flask quickly dissolves in a drop of water on the tip of the plastic tube. As a result, pressure in the flask decreases, and water rushes in because of a pressure drop relatively to atmospheric pressure.

Learn more

We do not feel the presence of atmospheric pressure because our bodies have adapted to life on the Earth's surface. In fact, though, a many kilometers thick atmosphere layer is constantly pressing on us.

The fact of atmospheric pressure existence is easy to verify. Prepare a large reservoir with water and immerse a transparent tall glass in. Let the glass fill with liquid. Then carefully turn the glass upside down and begin to raise it slowly, without taking the glass off from the reservoir. Water does not flow out from the glass because the atmosphere presses onto the water surface in the reservoir! In this case, atmospheric pressure is greater than the pressure of liquid in the glass, so the glass does not become empty. However, if you detach the glass from the water surface, the liquid will flow out and will be replaced with air.

In the cup with a thymol blue solution, atmospheric pressure acts on the surface of the liquid in a similar way. As soon as some ammonia dissolves in a drop of water on the tip of the tube, pressure in the flask falls below atmospheric. And then, the atmosphere can press the water into the flask through the tube, forming a fountain.

Creating an instant pressure drop in the flask is possible only because ammonia is highly soluble in water (about 700 liters of ammonia in one liter of water!). Very few gases would behave in a similar way at normal conditions. Carbon dioxide CO2, for example, is used for production of carbonated drinks. However, it takes of high pressure (above atmospheric) to dissolve a sufficient amount of it in water. That is why carbon dioxide forms bubbles when you open a bottle with soda.

The ability of most gases to dissolve in a liquid at elevated pressures can play a low-down trick with a man. Divers and deep sea expedition participants have to always keep it in mind. Water is much heavier than air, and at the 10 meters depth the pressure is twice higher than at the sea level. When a diver dives at great depths, gaseous nitrogen N2 dissolves in blood, which never happens at normal conditions. If a diver rises to the surface too fast, then the dissolved gas forms bubbles in blood vessels like it does in an open bottle of soda. This phenomenon is called decompression sickness and may lead to a very serious damage to the body including death.

Why does ammonia dissolve in water so well?

It is hard to imagine but we can dissolve up to 700 liters of ammonia in just one liter of water! Other gases can hardly compete with such characteristics. For comparison, only 30 mL of oxygen O2 can be dissolved in one liter of water, which is about 23 000 times less than in case with ammonia!

Why there is such a difference? In fact, ammonia molecules interact with water molecules and form so-called hydrogen bonds. These bonds are much weaker than chemical bonding, but they maintain gas molecules in dissolved condition. Moreover, there is also a chemical interaction of ammonia with water:

NH3 + H2O ↔ NH4OH ↔ NH4+ + OH-

On the contrary, oxygen O2, similarly to other gases, does not form hydrogen bonds. In addition, oxygen does not chemically react with water.

Learn more

What are these hydrogen bonds? It is quite a tricky question. Let’s try to find an answer without digging into complex scientific descriptions and calculations.

A hydrogen bond is a relatively weak bond between a hydrogen atom H and another atom in an adjacent or the very same molecule (the latter is called an intramolecular hydrogen bond). Note that the above mentioned hydrogen atom H is already linked to another atom (in our case, it is an «O–H» bond in a water molecule):

ammonia_fountain_hydrogen_bonds

If comparing a regular chemical bond between a hydrogen atom and another atom with hydrogen bonding, the most significant difference is in the distance between the atoms forming a bond and the energy of this bond (i.e. the amount of energy needed to break the bond).

In a water molecule, a hydrogen atom is situated approximately 1 Аo away from an oxygen atom it is connected with (Аo, or Angstrom, is a unit to measure very small lengths: 1 meter consists of 10 billion Аo). However, this same hydrogen atom also forms a hydrogen bond with an oxygen atom of a nearby water molecule, and the length of this bond is twice larger.

Interestingly enough, it is hydrogen bonding that makes water liquid at normal conditions.

Why is it so important not to turn over the flask?

Ammonia is about twice lighter than air, so it rises up. Ammonia from a test tube gradually accumulates in the flask and pushes air down. If you were to turn the flask upside down, ammonia would immediately fly away allowing for the air to replace it, and you wouldn't be able to continue the experiment with air.

Learn more

Ambient air seems lightweight and weightless, but it is only a first impression. In fact, it has weight! If you put a vacuum-pumped closed vessel (in which air has been sucked out with a pump) on the one scale and another closed vessel with air on the other scale, it would be obvious that air weighs more than nothing.

In 1811, Amedeo Avogadro, a scientist, found out that equal volumes of any gases at the same conditions contain the same count of molecules. Later, this principle has been called Avogadro's Law, in honor of its discoverer. Thus, the heavier are the gas molecules, the heavier is the gas itself.

Air is a mixture of gases. Air composition is 78.084% nitrogen (N2), 20.948% oxygen (O2), 0.934% argon (Ar), and 0.031% of carbon dioxide (CO2). The remaining 0.003% are neon (Ne), methane (CH4), helium (He), krypton (Kr), hydrogen (H2), and xenon (Xe). Therefore, air is slightly heavier than nitrogen and a little lighter than oxygen.

Some gases are very light. Helium He is one of the lightest gases. It is so lightweight that not only can it fly, but it can also lift something else. Thanks to this property, helium is used to fill balloons. The lightest gas, however, is hydrogen H2. Unfortunately, it is unsafe to use for hydrogen fun because it is extremely flammable.

Many gases are heavier than air, and quite often it causes disastrous consequences. Some settlements located in the lowlands surrounded by mountains have entirely died out because of natural emissions of toxic gases, such as hydrogen sulfide (H2S) and carbon dioxide (CO2). These gases are heavier than air. After breaking out from crustal faults or floating up from the bottom of a lake they displace air from above the ground surface, causing death of human and most animals.

One of the heaviest gases at normal conditions is sulfur hexafluoride (SF6), or Elagas. It is often used by nuclear physicists as an isolator in particle accelerators. Elagas is so heavy that if you "pour" it in a flat container and gently lower an aluminum foil boat on top, it would "float" on the gas surface. Sulfur hexafluoride is transparent, so it would create an impression that the boat is floating in the air.

Why does the liquid change its color?

Thymol blue dye belongs to a group of chemicals called indicators. Its solution changes color depending on the quantity of hydrogen ions (H+) in a thymol blue molecule. The indicator molecule has a very complex structure, so for simplicity we will use «Ind» to denote it. Thymol blue exists in three forms:

IndH2 ↔ IndH- ↔ Ind2-

Each of them colors a solution in a specific color: IndH2 – in red, IndH- – in yellow, and Ind2- – in blue.

In the cup, the indicator is mainly present in the form of IndH-, making the solution yellow. It happens because there is a certain amount of H+ in the solution.

When ammonia is dissolved in water, the quantity of free hydrogen ions H+ decreases, because they prefer interacting with NH3 molecules rather than straying alone in the solution:

NH3 + H+ ↔ NH4+

As a result, the indicator transforms into the Ind2- form, and the solution turns blue.

That's interesting!

What other gases can we use to make a fountain?

Efficient gas solubility in water is an important condition for obtaining a fountain. Ammonia is a successful candidate: at room temperature, it dissolves in the amount of 700 volumes in one volume of water. Only its close relative, methylamine (NH2CH3), is more soluble in water. A fountain obtained with methylamine and water stained with thymol blue, will turn out just as well as an ammonia fountain.

ammonia_fountain_ammonia

Nevertheless, besides ammonia and its close relatives, there are other gases that can be used for this experiment. Hydrogen chloride (HCl) and hydrogen bromide (HBr) are also highly soluble in water. In a single volume of water, one can be dissolve more than 500 volumes of hydrogen bromide or about 450 volumes of hydrogen chloride. Consequently, vacuum in the flask would be sufficient for the water to rush into the flask under the influence of atmospheric pressure. However, unlike ammonia, hydrogen chloride and hydrogen bromide would color the thymol blue solution in red or bright orange.