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Cooking an Egg in Chemistry Class (1 Favorite)

DEMONSTRATION in Observations, Chemical Change, Phase Changes, Physical Change, Specific Heat, Temperature, Heat of Combustion, Intermolecular Forces, Heating Curve, Boiling Point, Heat of Vaporization . Last updated May 24, 2021.


Summary

In this demonstration, students will observe the very high latent heat of vaporization for water by boiling water over a Bunsen burner in a paper cup to cook a boiled egg. The discussion can be extended to incorporate intermolecular forces to explain the unusually high boiling point of water, as well as heat of vaporization and specific heat capacity.

Grade Level

Middle School, High School

NGSS Alignment

This demonstration will help prepare your students to meet the performance expectations in the following standards:

  • MS-PS1-4: Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
  • HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

Objectives

By the end of this demonstration, students should be able to:

  • Explain how intermolecular forces affect the properties of water.
  • Describe physical and chemical changes that occur when a paper cup is used to boil an egg.

Chemistry Topics

This demonstration supports students’ understanding of:

  • Heat of vaporization
  • Phase changes
  • Boiling point
  • Heating curve of water
  • Physical and chemical changes

Time

Teacher Preparation: 30 minutes
Lesson: 30 minutes

Materials

  • Raw egg
  • Bunsen burner
  • Ring stand
  • Water
  • Paper cup (not plastic or Styrofoam, large enough to hold enough water to boil an egg, preferably with no plastic lining; could use sturdy paper, like a folder, to make an origami cup)
  • Thermometer

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Always use caution around open flames. Keep flames away from flammable substances.
  • Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
  • An operational fire extinguisher should be in the classroom.
  • Food in the lab should be considered a chemical not for consumption.
  • Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.

Teacher Notes

  • This demo can be used at almost any grade level and at various points in the year to illustrate different chemistry concepts. The student handout included with this resource is most appropriate to advanced middle school or high school students, but the demo can make an impact at an elementary school level as well.
  • For younger students, boiling water and cooking an egg can be used as examples of reversible and non-reversible changes caused by heating, and the students will be intrigued that the paper cup doesn’t burn.
  • At a more advanced level, students will be able to distinguish between physical changes (boiling water) and chemical changes (cooking the egg). You could add ice to the cup and discuss the full heating curve of water, including the latent heat of fusion as well as vaporization. Students could graph the temperature data and create the heating curve themselves.
  • It would probably be useful to do this demo after students have learned about bonding and intermolecular forces. A discussion of intermolecular forces and their effect on boiling point and heat of vaporization is included in the introductory reading. Water’s high specific heat capacity could be mentioned as well.
  • The background reading and prelab questions could be assigned for homework the night before and the demo could start with a discussion of the reading and questions.
  • Another way to start this lesson would be to ask a very generic question about water to activate students’ relevant prior knowledge (e.g. What do you know about water?). They might come up with things like its possible states of matter, different types/bodies of water (ex: salt water vs. fresh water, river, lake, ocean, etc.), melting or boiling point, that it’s required for life, that it is referred to as “the universal solvent,” etc. You could also ask students what they think will happen if you fill a cup with water and place it over a flame.
  • Other AACT classroom resources that could be used to teach these and similar topics include:

Procedures for demonstration:

  1. You can do this demonstration using a store-bought paper cup (preferred) an origami paper cup made from substantial paper (such as a manila folder) but it may leak. (You could get a student to make the cup to get them more involved.)
    • Please note: If your origami cup leaks, you will have to refill the cup periodically. If you need to refill the cup, use hot water or you will not achieve boiling temperature and therefore can only make a soft-boiled egg as opposed to a completely hard-boiled egg (8 to 10 minutes in boiling water). A soft-boiled egg will cook at 80℃ for 15 minutes.
  2. Fill your paper cup with water (collect the mass of the water if you wish to discuss this with students) and place it into a ring stand or on wire gauze above a lit Bunsen burner.
    • If you take the mass of the water, you should add a place for students to record the initial and final mass of the water near their data table.
    • You could take a second empty paper cup and put it over the Bunsen burner as well to show students that it isn’t a “trick” and there is nothing special about the cup (i.e. it is flammable!) other than it has water in it. If you do this, do it in a fume hood to avoid setting off the fire alarm and filling the room with smoke.
  3. Carefully place a thermometer in the water. (You may want to clamp it to a ring stand to ensure it doesn’t fall out or knock the cup over if the cup is small.)
  4. Once the water is boiling, they should note that the temperature remains stable starting at time “0” in their data table. (This is the latent part of the latent heat of vaporization – the temperature doesn’t change during the phase transition from liquid to gas.)
    • You could start measuring the temperature before the water boils for students to observe how the temperature increases to a point and then holds steady once it is boiling. If you decide to do this, be sure to adjust the data table accordingly.
  5. Add the egg and let it cook for 10 minutes. (Set a timer – preferably one that the students can see.)
  6. Each minute, announce the temperature of the water so that students can record it in their data table.
    • You could use this as a chance for students to practice their measuring skills and have student volunteer read out the temperature data, particularly if you have already gone over reading measuring equipment to the appropriate number of significant digits.
  7. Students should also record additional observations during the 10 minute demo – some examples a teacher could suggest are: do you notice changes in the cup? The water? The egg? Describe what you see happening in the cup. Etc. You could have each student (or as many students as volunteer) come up to observe the demo more closely and make an observation.
  8. After the ten minute timer is up, remove the egg and crack it open to show students it is cooked through.
    • Check with the school nurse for egg allergies among your students before doing this demonstration.
  9. If you measured the mass of the water prior to boiling it, you may want to measure the mass again, and discuss any changes with students.

References

For the Student

Lesson

Background

Water is an extremely important substance to life here on planet Earth, more than two-thirds of which is covered in water. All living things need water to survive. More than half of your body weight comes from water, and you wouldn’t last much longer than a few days without a way to replenish your body’s water supply.

Besides being critical to living creatures, water is also an interesting substance because it is one of very few substances that can exist as a solid, a liquid, and a gas at relatively “normal” temperature and pressure conditions. Most substances that have molecules similar in size to water molecules are gases at room temperature, but water molecules are held together by a strong intermolecular force called hydrogen bonding. Hydrogen bonding occurs when a highly electronegative atom (oxygen, nitrogen, or fluorine) is covalently bonded to a hydrogen atom, creating a polar covalent bond. This results in very strong dipole-dipole interactions between the molecules called hydrogen bonding (as long as the polar bonds are arranged to create asymmetry around the central atom). This force keeps water molecules closer together over larger temperature ranges than other similarly sized molecules, which allows water to exist in solid and liquid states in temperatures commonly experienced on earth. This means that its melting and boiling points are much higher than similar compounds that do not experience hydrogen bonding.

In addition to causing water to have an unusually high boiling point, the large amount of energy required to separate water molecules due to their hydrogen bonding also gives water a relatively high heat of vaporization – the amount of energy required to turn a certain amount of a substance from liquid to gas. This is why your body sweats to keep cool, and why you feel cooler when you pour water on yourself – the water on your skin evaporates when it absorbs heat energy from your body, and transferring the heat into the water and away from your body cools you down. This also makes boiling water a good way to cook food, because it absorbs a lot of heat energy before it all boils away, and it can transfer some of that energy to cook the food you place in the water.  That is how we are going to boil an egg in chemistry class!

Prelab Questions

  1. Think about when you use water throughout your day. List at least 5 different ways you use water in your daily life. (Be sure to consider all the forms water can take!)
  2. Define the following terms:
    1. Heat of vaporization
    2. Boiling point
    3. Hydrogen bonding
    4. Chemical change
    5. Physical change
    6. Specific heat capacity

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Always use caution around open flames. Keep flames away from flammable substances.
  • Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
  • Food in the lab should be considered a chemical not for consumption.
  • Wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.

Data and Observations

As your teacher conducts the demonstration, you should record the temperature data as well as observations regarding water’s physical state and any changes you see in the paper cup or the egg. Particular note should be paid to the paper cup – whether the cup is store-bought or made from folded paper, what kind of paper it is made of, etc. These subtle observations have real implications for this demonstration.

Time (minutes)
Temperature (℃)
Observations
0
1
2
3
4
5
6
7
8
9
10

Analysis

  1. We just used boiling water to cook an egg. Classify each of those processes – boiling water and cooking an egg – as a physical or chemical change. Explain your classification for each.
  2. What did you notice about the temperature of the water once it started boiling?
  3. Chemists use the melting point and boiling point to identify substances because these are fixed points and are relatively easy to measure. Given what you observed while the water was boiling, explain why melting and boiling points are relatively easy to measure.
  4. For a fire to start, three conditions need to be met: 1) a high enough temperature, 2) sufficient fuel, and 3) sufficient oxygen. An empty paper cup would burn easily if exposed to a flame under normal conditions. The paper cup with water in it did not burn because it was lacking one of those three factors. Which do you think it was, and how did having water in the cup play a role in limiting that factor? (Hint: Think about what you saw in this demonstration to determine what the main difference is between an empty paper cup and one full of water – temperature, fuel, or oxygen?)
  5. Imagine that you had a substance similar to water, except that it had weak intermolecular forces, rather than strong hydrogen bonding. Describe how the weaker intermolecular forces would affect the boiling point and the heat of vaporization of that substance. Would this substance be useful for cooking, the way water is? Why or why not?
  6. Sometimes the heat of vaporization is referred to as the latent heat of vaporization. What does “latent” mean, and why is it used in reference to heat of vaporization?

Conclusion

In 1-2 paragraphs, explain in your own words what you learned from this activity about water and its unique properties.