The Egg in a Flask Mystery (Day 1 of 2)

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SWBAT develop an understanding of the nature of science by developing a model, supported by evidence, to explain how the egg gets into a flask.

Big Idea

Get your kids excited to be in science by presenting the egg challenge lesson. Students will develop important NGSS practices by determining how the egg got into the flask!


The nature of science has often been taught in a systematic fashion, starting with the scientific method and trickling down to cover topics like measurement, metric conversions and other such skills.  Often these practices aren't covered much more in class that year and students are left with a disjointed understanding of how scientists make discoveries and then attempt to explain them through the creation of models. 

In this unit, I hope to link lessons that expose my students to actual mysteries and issues that encourage their appreciation and knowledge of the nature of science.  Each lesson--which may take several days--will present a STEM demonstration or other activity that encourages students to develop a working knowledge of the 8 NGSS Science and Engineering Practices.  I will then flush out the specific skills that I want students to work on during each lesson, mainly focusing on argumentation and developing models supported by evidence.

In this lesson, I present the classic 'Egg Suck' activity to my class and students then work in teams to help solve the mystery. 

Note: Due to the dangers with the flame, most follow-up experiments will have to be performed by the teacher.  However, the pivotal mistake that teachers can make in the activity, myself included, is to tell students that their idea won't work, as opposed to actually testing it (assuming that their ideas are testable and safe). 

Overview of Lesson (For Teacher)

The egg suck activity doesn't suck.  Literally, the egg is not sucked into the flask, it is pushed in when the warm air molecules--created by the lighted matches being dropped into the flask--exit, and the higher pressure from the air outside pushes the egg in.  My mission in this lesson is to:

1.) Have students to create initial mental models to explain the egg phenomenon, which will be shared with their peers;

2.) Have students collect qualitative and quantitative data through observation and/or have them research various natural phenomena, such as the effect of heat on air or properties of matter, to help establish a more developed model;

3.) Use the evidence collected to alter their original mental models into a descriptive model that can be argued/supported with evidence.

Prior to beginning the lesson, please gather all required materials (see materials section) and make sure that you don't have any students who may have an egg allergy.  Students do not have to touch eggs in this activity. Alternatively, you may show this video that depicts the demonstration.

The lesson unfolds in the following order.  First, I ask students to make a prediction about what they think is going to happen, prior to performing the demonstration.  I then give each student the opportunity to think critically about how the egg got into the flask, and ask them to draw a picture (model) to help explain the phenomenon.  Since my classroom is arranged into groups of 4-5 cluster of desks that face each other,  students next get an opportunity to share their ideas with their respective group.  

The next phase of the activity is for each group to work together to use inductive reasoning to create a new conceptual model.  In the final phase, each group shares their new models and then the class develops a final, consensus model.  Assessment of student learning occurs when students compare and contrast their original and final models for homework.

I follow the NSTA's (go to slide 55) suggested framework for Developing and Using Models in science classrooms in this lesson, as well as other lessons in my curriculum.  This lesson is focused around getting students used to using models to formalize their thoughts.   


  • 1 or 2 500 mL Erlenmeyer Flask per class (They get egg debris and moisture in them and can generally only be used once per demonstration)
  • Enough medium or large hard boiled eggs to do the demonstration, at a minimum, of twice per class (I boil mine at home the previous night and bring them to school--I add an alert on my smartphone so that I don't forget)
  • One box of stick matches
  • Rubber stoppers to seal the top of flasks to prevent smoke from bellowing out
  • Fire extinguisher 
  • Safety glasses for demonstrator--keep kids far enough away.  If they are safe distance then the only real safety issue will be broken glass, if the flask drops.  Instruct students to remain in place if glass breaks and that you will pick up the pieces--they should not touch broken glass.  
  • You may want to alert the teachers in the building that there may be a faint smell of burning matches throughout the day.  I like to cover the flask after the demonstration with a rubber stopper and then take the used flasks outside to air out during my prep period.  This helps keep the ambient air in your room healthier and less smelly.  

Demonstration and Central Question

5 minutes

After welcoming students to class, I begin this lesson by stating, “Today we are going to practice science by developing a model to explain a phenomenon witnessed in class.”  I explain how the demonstration will progress--Light matches, drop them into the flask and immediately place the hard boiled egg on top of the opening in the flask.  

Now students record predictions about what they think is going to happen during the demonstration.  I then ask students to share their predictions with the class.  After we have shared what we believe will happen, I perform the egg demonstration in front of the class, by dropping matches into the flask.  I save the birthday candle part of the experiment for the end of the second day of the lesson to put students' thinking to the test.   

The video below shows how the predictions are recorded on the board and how students record their predictions and observations in their notebooks.

Developing Initial Model and Peer Sharing

10 minutes

Now that students have experienced the demonstration, they are now held responsible for creating an initial conceptual model that explains how they think the egg got into the flask.  I have begun using science notebooks as a way for students to record their thoughts and track their learning and will be unveiling best practices as the year progresses.  In the mean time, I have each student record their prediction in their notebooks.  I then ask them to create drawings (model) that 1) depicts what happened in the demonstration; I advise them to record the events in sequential order.  Remember: this is their model and their notebook, therefore, it is prudent to allow them to create their models in a way that makes sense to them.  For example, if they want to make a picture for each step--that is perfectly acceptable, and probably a logical way to go about documenting their observations and 2) demonstrates students' understanding about how they believe the egg got into the flask.  This is a good time to have students revisit their logic behind the predictions that they made.  Ask them to think about the 4 W's (What, Why, When and Where).  This will help them establish a cause and effect relationship for the observed phenomenon.  It may take students some time to think this through, so don't be alarmed if they sit and ponder prior to jotting down ideas.  They are most likely not dawdling, but certainly check in with those that seem to be after about 2 or 3 minutes.  

Once students have recorded their models, it is time for them to share their initial explanations with their group members.  I have students sit in groups of 4 desks that face each other, promoting constant collaboration.  There are times when I may have to arrange desks to have a 5th desk.  In that case I just stick the desk at the end of the cluster of 4 desks perpendicular to the other 4 students.  Each student gets 1 minute to share their model, while other students jot down questions that they have about what they are hearing in their notebooks.  This will help spark group discussions in the following phase.  I circulate around the room to assure that all students are sharing and that students are recording their sentiments about their peers ideas in their notebooks.   

Empirical Investigations & Model Elaboration/Revision

15 minutes

In this section I want to provide an opportunity for my students to think of evidence that they can collect from the investigation.  I will ask students to come up with observations or measurements that we can do that may help us understand what is happening.  

Students usually want to know:

1) What does the egg feel like (again, remember allergies)?  They can compare this to an egg with the shell on it. 

2) What is the effect of heat on the flask, air, and egg?  (Since it happens so fast, you may want to have inexpensive IR thermometers available)  Alternatively, you can use the sensors if your department owns them.  You may also be able to rig a way to at least see if the matches change the temperature on the inside of the flask.  Also, don't forget to measure the air temperature on the outside of the flask. 

I have students record all of their evidence into their science notebooks.  You should encourage them to collect any information that they think is pertinent to explaining the egg activity.  Just because you know that it may not help explain, it doesn't mean that your students shouldn't collect the information.  

Of course, if they want to collect information that is completely off the wall then redirect their ideas.  We want to encourage science practices and develop an appreciation for the nature of science so encourage their ideas and let them figure out--with their group mates-- what is relevant.

The lesson changed course at this point, in response to student needs. This is covered and explained in detail in my reflection.


Ask students to develop a new model that clearly explains--to the best of their ability--how the egg got into the flask, using the information gathered from class.  

They should record their models, which will be shared with their group first thing during the next class, in their science notebooks.  Encourage students to write captions in their models to help their peers understand.