Discrepant Event: Egg in a Bottle
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DISCREPANT EVENT: EGG IN A BOTTLE
Introduction: This classic experiment engages students in a fascinating and unexpected display of a chemical reaction causing unequal air pressures in a simple closed system. A peeled, hard-boiled egg is pushed into a glass bottle due to lowered air pressure inside the bottle. The egg can then be forced out of the bottle when the air pressure inside the bottle is increased.
Subject Area: Physical Science - grade 7 or 8. Chemistry - grade 9.
Minnesota State Standards (that this experiment can tie into):
Grade 7 - Strand 2. Physical Science - Substrand 1. Matter Standard 1. The idea that matter is made up of atoms and molecules provides the basis for understanding the properties of matter. Benchmark 7.2.1.1.3 - Recognize that a chemical equation describes a reaction where pure substances change to produce one or more pure substances whose properties are different from the original substance(s).
Grade 8 - Strand 2. Physical Science - Substrand 1. Matter Standard 2. Substances can undergo physical and chemical changes which may change the properties of the substance but do not change the total mass in a closed system. Benchmark 8.2.1.2.1 Identify evidence of chemical changes, including color change, generation of a gas, solid formation and temperature change.
Grade 9 CHEMISTRY - Strand 2. Physical Science - Substrand 1. Matter Standard 3. Chemical reactions describe a chemical change in which one or more reactants are transformed into one or more products. Benchmark 9C.2.1.3.4 Balance chemical equations by applying the laws of conservation of mass and constant composition. Benchmark 9C.2.1.3.5 Use the law of conservation of mass to describe and calculate relationships in a chemical reaction, including molarity, mole/mass relationships, mass/volume relations, limiting reactants and percent yield. Benchmark 9C.2.1.3.6 Describe the factors that affect the rate of a chemical reaction, including temperature, pressure, mixing, concentration, particle size, surface area and catalyst.
Topics Covered: Combustion Chemical reactions Composition of air Air pressure variability The Law of Partial Pressures
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Materials: At least two hard-boiled eggs, peeled* At least two empty glass bottles with openings slightly smaller than an egg.* Vegetable oil Strips of paper as long as the height of the bottle Matches or lighter (Optional) Alka-Seltzer *Note: Old-fashioned milk bottles are the ideal size to use for this experiment but are difficult to find. If a bottle cannot be located that has a mouth slightly smaller than an egg, a water balloon can be substituted for the egg and therefore a larger-mouthed bottle can be successfully used.
Engage: Divide the class into two and assign a “job” to each side: Every time you hear the word “suck” I want you to say “NOTHING IN THE UNIVERSE SUCKS!” Every time you hear the word “vacuum” I want you to say “THERE IS NO SUCH THING AS A VACUUM!”
Procedure: 1. Lightly oil the rim and the inside surface of the bottle necks with the vegetable oil. Place each egg on the mouth of a bottle, showing that they are too big to fall in.
2. Say “I am going to put a flame inside the bottle and cover the opening of the bottle with the egg. What do you think will happen?” Anticipated answers: “the egg might jump off”, “the fire will go out”, “the bottom of the egg will get burned”, “the bottle might crack”, etc.
3. Ignite a strip of paper, lift the egg up, and place the burning paper in the bottle. Wait a second for the flame to heat the air inside the bottle and replace the egg. The flame will be extinguished. The egg will vibrate and will be forced into the bottle.
4. Ask students to observe carefully while you repeat with the second egg and bottle.
5. Ask: “How can we get the egg out of the bottle without cutting it up?”
6. To get the egg(s) out of the bottle(s) whole: invert the bottle and let the egg fall into the bottle neck. Arrange egg so that narrow part is closest to bottle neck. Take a deep breath and blow air into the inverted bottle. Then quickly hold the bottle pointed away from all people. The egg should shoot out of the bottle. (If it doesn’t, try blowing again.)
Questions and Scientific Explanations: 1. Why did the egg get pushed inside the bottle? The air pressure outside of the bottle was greater than the air pressure inside of the bottle.
2. What did the burning paper do to the air inside the bottle? The flame heated the air and expanded it. Putting the egg on top extinguished the flame, which caused the air in the bottle to cool and contract, taking up less volume. The pressure on the outside of the bottle was then greater than the pressure inside the bottle and the egg was forced into the bottle. In PV=nRT, Pressure (P) is proportional to Temperature (T). If T goes down, P goes down.
Chemical Reaction: Air is made up of 79% nitrogen (N2) and 21% oxygen (O2). The partial pressure of nitrogen + the partial pressure of oxygen = 1 atmosphere. Before the paper was ignited, the pressure was equal inside and outside the bottle. The combustion reaction converted the oxygen (02) in a gaseous state to water (H2O), which takes up less space. Because the egg stopped the flow of air into the bottle, the pressure couldn’t equalize and was lower inside the bottle. The egg was pushed in.
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3. What did the egg do before it went into the bottle? Why? The egg vibrated. The burning paper heated the air in the bottle and expanded it, pushing some of the air under the egg and out of the bottle, causing it to vibrate.
4. Why did water condense on the inside of the bottle after the flame went out? The water vapor in the warmed air condensed when it contacted the colder walls of the bottle.
5. Why did blowing air into the bottle cause the egg to be forced out? Acting like a one-way valve, the egg allowed the blown air in but sealed it from rushing out. Blowing air into the bottle increased the air pressure inside so that it was greater than that on the outside of the bottle. The egg was “pushed” out because of that excess pressure.
6. Is there another way to get the egg out whole? Why would that work? The bottle could be heated while the egg sits against the neck. The heated air would expand and force the egg out of the bottle.
Alka Seltzer and a little water could be added to the bottle while the egg sits against the neck. The CO2 given off by the Alka Seltzer would expand the air in the bottle and force the egg out. SAFETY NOTE: Do not try using Alka Seltzer with Erlenmeyer flasks or other bottles with similarly thin glass walls, as the pressure buildup could potentially shatter the bottle. Wear safety glasses.
Misconceptions to Be Addressed: 1. A vacuum is created inside the bottle. The change in air pressure DOES NOT create a vacuum to suck the egg into the bottle. The greater pressure outside the bottle pushes the egg into the bottle.
2. The oxygen is all burned up by combustion.
The oxygen is not completely consumed by combustion. It is converted to CO 2 and H2O, as evidenced by the condensation inside the bottle when the warm air contacts the cooler walls of the bottle.
Follow-up Activities: This experiment could be used as an introduction to physical science or chemistry lessons involving the properties of air or gases as well as chemical reactions, chemical changes, and chemical equations.
Describe what chemical changes took place in an essay.
Explain the pressure decrease using only chemical equations and diagrams.
Explain Dalton’s Law of Partial Pressures in relation to this experiment.
Safety Issues: The matches or lighter should be kept in the teacher’s possession at all times. Burning paper requires caution. Wear safety goggles When extracting eggs, aim bottles toward floor and away from people, as the eggs can exit with force. If using Alka Seltzer to extract eggs, avoid using bottles with thin glass walls (such as Erlenmeyer flasks) as they could shatter under the pressure.
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