As we continue our unit of “The Chemistry of Life,” we learned today about the amazing properties of water. Before we started the lesson, we brainstormed as a class as many words as we could come up with that begin with the prefix co-. You all did a great job! Words such as cooperative, co-worker, or co-exist were among the most common. From there, students had the task of deciding what they thought this prefix co- meant. Based on the words that we brainstormed, students built on this knowledge to define co- as meaning “together.” Awesome job once again! This was a great COllaborative inquiry activity as students worked together positively to make their own learning by working with what they already knew.
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| How does a bug walk on water? |
The reason why we needed to know what this prefix meant was because we were introducing the concept of cohesion, a property of water. Students had already learned that a water molecule, H2O, is made up of two hydrogen molecules, and one oxygen molecule. But, when we see water, we don’t just see one molecule, we see millions of them together! Well, how do these molecules work together? Have you ever seen a bug walk on water? Pretty cool, right? But, why don’t they fall right through like we do when we jump in water? We later learned that this is because of COhesion! A property that only water can do.
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| Hydrogen bonds between water molecules |
All I had to do was show students this word and they already knew the basics of what it most likely meant, as they took their knowledge of the prefix co- and decided it must mean the water is together. This was great as students easily translated this basic definition to a formal scientific definition of cohesion- molecules sticking together. From there, students were extremely invested as they have almost been the teacher for most of the lesson already! We next learned that cohesion is when the opposite charges of a water molecule, oxygen being negatively charged and the two hydrogen atoms being positive, attract to each other, forming a strong hydrogen bond. So, when you see a bubble of water on a plant, it is tons of hydrogen bonds forming between oxygen molecules and sticking together. From this, students were then asked to work in small groups and justify how a bug may stand on top of water without falling in. Several groups were correct in that the legs of a bug do not break the strong hydrogen bonds between water molecules, allowing them to stand on top!
This lesson was successful in using Vygotsky’s (1978) Zone of Proximal Development (ZPD) as the lesson was geared to what the students could do on their own, and then knowledge was pushed using collaboration and teacher mastery guidance to further learn new concepts and vocabulary. This was seen as successful as students were engaged and motivated, while working with new information and forming deeper comprehension. Now that students have proven they are true scientists with the simply concepts of cohesion, it is time to take this knowledge a step further by conducting a lab. This lab is called “The Penny Lab.” The materials and procedures are below.
Materials
· 1 Penny
· 1 pipette (provided by teacher)
· Cup of water
· Cup of water with soap mixed in
Procedures
1. Place the penny face up on a flat surface
2. Fill the pipette with the water only
3. Drop water onto the face of the penny slowly, counting every drop
4. Continue to count and drop water until the water spills off the penny
5. Record the number of drops and repeat for a total of 3 trials.
6. Once you have completed 3 trials using water only, complete the same experiment using the water and soap mixture
7. Repeat and record for a total of 3 trials
8. Average the trials for the two groups and draw conclusions
Make this graph in your science journal to keep your data.
Type of Water | # of Drops | # of Drops | # of Drops | Average of 3 trials |
Water only | ||||
Water and Soap Mixture |
Once you are completed with the trials, please conclude as to why you think the water and soap mixture might not be able to hold as much water on top of the penny. Use your content knowledge from the lesson of hydrogen bonds and cohesion to defend you answer.
Vygotsky, L. S. (1978). Mind in society: The development of higher psychological processes. Cambridge, MA: Harvard University Press.
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