Expt 013 -- Hero's Fountain

Fountains have seeming ageless interest. See Fountains: The World of Water to learn more about fountain history, design, architecture, hydraulics and usage throughout the world.

Chemical Concepts

1. Energy in conserved.
2. Potential energy may be converted into kinetic energy.
3. The activation energy of a process is the extra energy required to change from one stable state to another. Extra energy is frequently required to initiate a change even when the change is exothermic.
4. The energy of reaction is the difference in potential energy stored in chemical bonds before and after reaction.

Safety

• Hot glass and hot objects can cause burns. Hot glass and cold glass look exactly alike. Hold a finger near a previously-heated object for several seconds before touching it to detect heat. Do not grasp hot objects.
• Use extreme care and plenty of glycerin when inserting tubing in rubber stoppers. Always hold the stopper from the side.

Procedure

Set up the apparatus at one side of the lecture table where it can continue without interfering with other activities.

1. Fill the left hand bottle with water and place it about 20 cm higher than the right hand bottle, insert stoppers securely, then pour about 500 mL of water in the funnel. Carefully, mark the water level in each bottle.

   !!!Click here to See Movie.

   !!!Click here to See Picture. An enlarged scrolling view of apparatus.

   If there is any problem, set the lower bottle on the floor until the fountain starts up. While it is tempting to leave the bottle on the floor spouting a tall column of water, the funnel may go dry because so much water is spattered about the laboratory that the tubes drain faster than the funnel is replenished.

2. If the fountain is irregular, flick the tip with your finger. If the tip is aligned and clean, a fine vertical stream disperses into many smaller streams above the tip.

   !!!Click here to See Movie.

3. Move the lower bottle to different levels to illustrate the change of potential energy (the water levels) to kinetic energy (the velocity of the water on exit). The kinetic energy changes back to potential energy as demonstrated by the height of the fountain. Query students about the energy changes at each point.

   !!!Click here to See Picture.

4. Optional: From a distance, charge an inflated balloon by rubbing it against your hair. Hold it toward the fountain. On a dry day, the static charge affects the fountain from several feet away.

   !!!Click here to See Movie.

5. After the fountain has run a while, point out to the students the water levels in the two bottles. It takes a long time to show much difference. To accelerate the change you may remove the narrow glass tip. The fountain effect is lost but you can perceive a change in the water levels within 3 minutes.

   !!!Click here to See Movie. In order to display the siphon action, the tip is removed, and the time-lapse movie is accelerated 30 times.

Questions

1. Label the point in the apparatus where water has the lowest potential energy in the system.
2. Label the point in the apparatus where water has the highest potential energy.
3. Label the point in the apparatus where the water has the minimum potential energy required to transport it through the funnel to the lower bottle.
4. Label the point in the apparatus where water has the highest kinetic energy.
5. For chemicals to react, stable molecules must acquire enough potential energy to break the old bonds and form new ones. The potential energy required in this state is the activation energy. Label the point in the apparatus that is analogous to the potential energy hump called the activation energy.

Handout

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 013 Hero's Fountain

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 013 Hero's Fountain

Watch the movies.

Label the diagram as requested in the Questions.

Curriculum-

• This activity fits into discussions of energy, particularly potential energy. For beginning students, you may wish to limit discussion to energy changes.
• Analogies between the fountain and those abstract activation energy level diagrams in kinetics chapters help students picture the levels. Couple this activity with some exothermic reaction that requires activation energy to clearly illustrate the significance of the activation energy. The burning of a wax candle is an excellent comparison.

Activity-

Demonstration - Student or Teacher

This demonstration works well if you set it up early in the period over at the side with minimal explanation. Later in the period when students can see the difference in the levels explain the energy changes. Energy level diagrams and a diagram of the apparatus are included in the Figures if you wish to have students label these diagrams when you return to the demonstration.

Safety-

• Hot glass and hot objects can cause burns. Hot glass and cold glass look exactly alike. Hold a finger near a previously heated object for several seconds before touching it to detect heat. Do not grasp hot objects.
• Do not allow students to insert glass tubing into rubber stoppers. They may cut themselves severely.
• USE PLENTY OF GLYCERIN WHEN INSERTING THE TUBING THROUGH THE STOPPERS. Place the stopper on the desk and push the tubing into it. Hold the stopper from the side to finish inserting the tubing.

Time-

Teacher Preparation: 5 minutes (Construction 15 minutes one time.)

Class Time: 15 minutes (Start early in the period to allow time in order to come back and check the level after 20 minutes.)

Materials-

• 3 2-L soda bottles
• 3 2-holed stoppers (#3) to fit bottles
• 80 cm glass tubing (6-mm OD) or 80 cm rigid plastic aquarium tubing -- 5-mm OD and 12 cm glass tubing
• water

See Lab Hints for construction information.

Optional:

• a balloon

Disposal-

Save apparatus for future demonstrations.

Lab Hints-

Do not add coloring to the water. During the demonstration, your surroundings and clothes are spattered with a fine mist of the water (with the food coloring if included). Colorless water is more visible in the laboratory than on a two dimensional video so the coloring is not an asset.

Construction (time - 15 minutes):

1. Score and break a glass tube into six pieces -- 38 cm, 32 cm, 12 cm, 4 cm, 4 cm and 4 cm. Fire polish all ends and allow to cool.
2. Heat and stretch the 12 cm length to make two finely tapered pieces. Use glass for this one.
3. Cut two lengths of flexible aquarium tubing each about 80 cm long. Cut off the top third of a 2-L soda bottle, and assemble the fountain as illustrated below

USE PLENTY OF GLYCERIN WHEN INSERTING THE TUBING THROUGH THE STOPPERS. Then rinse the glycerin off when you're done. Hold stoppers by the sides.

Observations-

• Initially the pressure in each bottle, A (upper) and B (lower), is equivalent to atmospheric pressure. As water is poured into the fountain bowl on top, it drains down through hose #1 into the lower bottle (B) and creates additional (hydrostatic) pressure there. If, for example, the water level in the bowl is 100 cm higher than the water level in bottle B, then the air pressure inside B must increase to 1 atm + 100 cm water. Since the air pockets in A and B are connected by hose #2, the pressure in bottle A must also rise to 1 atm + 100 cm. In other words, since the pressure outside the fountain is only 1 atm, the pressure in bottle A should be able to support a column of water 100 cm tall. Since the tapered nozzle is only about 20 cm above the water level in bottle A, the water is easily pushed up through it -- with enough pressure left over to spray droplets upward, creating the fountain effect.
• If bottle B is lowered even further, then the hydrostatic pressure increases inside B, and consequently inside A as well, causing the fountain to spray even higher. Conversely, if bottle B is raised relative to the bowl, the hydrostatic pressure decreases, and the fountain spray diminishes. If we use "x" to denote the vertical distance between the water level in the bowl and the water level in bottle B, and we use "y" to denote the vertical distance from the water level in A up to the top of the tapered fountain head, then the fountain always sprays upward with a force proportional to x - y. As soon as y equals or exceeds x, the fountain stops.
• Note that the water draining down from the bowl into bottle B is being replaced by a more or less equal volume of water spraying up from the fountain into the bowl. Thus, once the fountain is started, it should run continuously without any additional priming. At first glance this may appear to be some kind of perpetual motion machine. But, since water is draining downward through hose #1 and only air is flowing back upward to replace it through hose #2, the fountain does not flow perpetually, but only until the water in bottle A has drained out completely or, if the bottles are pretty much on the same level, until y = x, as discussed above.
• Another way to visualize the fountain is in terms of potential and kinetic energy: The water is at its lowest potential energy in the lower bottle. The water in the upper bottle does not begin flowing until the fountain is "activated" by adding additional potential energy to the system by pouring water into the funnel. Once the funnel and tubing is full, the potential energy between the upper and lower water levels in the full bottles determine the length and height of the demonstration. The gas pushed out of the bottom flask by water in turn pushes water out of the upper flask changing potential energy into the kinetic energy of the water as they exit the glass tip. At the tip the kinetic energy of the water is largest. The potential energy of the water is largest at the highest point in the stream of the fountain of water. All of the water, which has enough energy to emerge from the glass tip, can flow into the lower bottle.
• The potential energy levels may be used to illustrate the potential energy diagrams frequently used in kinetic explanations. The energy difference between the water levels in the bottles is analogous to the heat of reaction (the difference in chemical potential energy between the reactants and products). The potential energy of the water at the glass tip is analogous to the activation energy. Both are potential energy humps that must be overcome even when energy is stored. The energy is added to start the system, but the system sustains itself with the difference in potential energy of the initial and final energy states. In the end, no water is at the glass tip and no molecular fragments are at the activation energy.
• The optional charged-balloon variation illustrates a very different phenomenon: how an electrostatic field can induce a polarity in another object. The electrically charged balloon attracts opposite charges in the water droplets and repels like charges. Even a slight migration of these charges can establish an induced polarity in each individual water droplet. Since they have been polarized, the droplets tend to coalesce into larger droplets and ruin the spray effect of the fountain. What is most remarkable is that this effect can be observed even when the charged balloon is held several feet away.

Answers-

Key Words 1-

kinetics, activation energy, potential energy, kinetic energy, electrical energy, thermochemistry, energy of reaction