Introduction:

At some point in time we have all boiled water. Generally speaking it is an easy enough task to complete. However, have you ever wondered what is inside of the bubbles that are produced during the boiling process? To determine what people think about this I conducted a survey with three people of varying ages and levels of higher education. I wanted to see if the average person, who is not a science major, understands what happens to particles of matter during a change of state.  

I prompted each person with the following:"Hannah is boiling water in a glass tea kettle. She notices bubbles forming on the bottom of the kettle that rise to the top and wonders what is in the bubbles. She asks her family what they think, and this is what they say:

Dad: "They are bubbles of heat." 

Calvin: "The bubbles are filled with air." 

Grandma: "The bubbles are an invisible form of water." 

Mom: "The bubbles are empty - there is nothing inside of them." 

Lucy: "The bubbles contain oxygen and hydrogen that separated from the water."

Which person do you most agree with and why?"

Results:

Person #1: Renee - early 50's with some college 

Renee said she agreed with Mom's thought process that the bubbles are empty and there is nothing in the bubbles because they just formed from the heating of the water. I proceeded to ask her what heat came from and she told me that heat comes from the stove - it is a form of energy. I asked her what happens when you heat water for a long period of time and she said it evaporates and produces water vapor.      

Person #2: Josh - early 20's with no college

Josh said he thought that Lucy was correct and the bubbles contained oxygen and hydrogen that separate from the water. He furthered this by stating that there was a chemical reaction that occurred when the water was heating up and evaporating. He urged that during the boiling process evaporation occurs so that hydrogen and oxygen are put back into the air.  

Person #3: Geysa - early 40's with no college

Geysa said that she agreed with Grandma about the bubbles being an invisible form of water. She said that when water boils evaporation occurs, which produces water vapor. 

Evidence: 

Please view The Phase Changes of Water Song on Youtube to understand what happens when water changes state. <http://www.youtube.com/watch?v=lTKl0Gpn5oQ>. 

Conceptual Understanding:  

I was fascinated by each person's ability to think through the boiling process to determine what could be in the bubbles. Even the people who guessed wrong to start somehow, maybe through questioning, seemed to make their way towards understanding the change of phase of water. Everyone seemed to understand that when water boils evaporation takes place, which was not shocking since each person is intelligent. I was kind of surprised that Josh thought that water boiling was a chemical reaction though - as a science major I know you need to mix different substances together for a chemical reaction to take place. In addition, I was happily surprised to see that Geysa got the correct answer right from the start. I was also pleasantly surprised that Renee seemed to work her way from the wrong answer to the right answer because she kept telling me she never thought about this kind of thing. From this survey, with this particular group of people I could assess what is in the bubbles on a higher level because each person had an idea of what occurs during evaporation, as well as that water changes state. Without actually observing water boiling in front of them it may have been difficult to imagine the steam that comes off of the boiling water, so it may have been easier to overlook the change of state of water from a liquid to a gas.

Activities could be used to improve societal understanding about the change of states of matter. For example, boiling a kettle of water with a balloon put around the spout could be used to show the change of state of water. When the water is not boiling the balloon with be deflated, but when the water boils the water changes from a liquid to a gas and fills the balloon so it inflates. Also, observing the environment around us could be used to investigate the change of state of water. For example, during the summer after a rainstorm there are puddles on the pavement, but when the sun comes out after a period of time the water disappears, which shows the process of evaporation where water changes from a liquid to a gas.   

Conclusion: 

While only one person who was surveyed got the correct answer from the beginning, each person had a valid reason for believing what they thought to be inside of the bubbles. I also helped to talk both Renee and Josh through the boiling process after they told me their thoughts so they would understand that the bubbles are invisible water molecules because the water changes state in the boiling water to form a gas, which comes out of solution as steam. To further understand the change of state of water I found a video on Youtube to reinforce the ideas demonstrated when boiling or freezing water. 

References: 

Physical Science Assessment Probes - www.nsta.org/permissions