After it was over I felt utterly exhausted. Developing my first laboratory experience that met the Performance Expections of NGSS required time and energy. Was it worth it? Absolutely.
|Finding the melting point of an unknown solid.|
After studying the NGSS Performance Expectations over winter break, I decided that an upcoming unit on Bonding and Intermolecular Forces might provide an opportunity to tackle HS-PS1-3. The performance expectation for this standard required students to “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.” By the time my students were asked to plan this investigation, they had already studied some topics that would improve their chances of successful achieving this standard. The following topics were covered in class prior to this point:
- Electrolytes and conductivity of solutions (See 12/15/14 post)
- Ionic versus covalent compounds
- Polar and nonpolar covalent structures
- Intermolecular forces
|Grinding the compound into a fine powder|
I provided students with basic information that would guide their lab design. They would be given two different white solids for the experiment. The unknown substances could be ionic or covalent compounds. Their goal was to design a lab that would allow them to compare the strength of attractions between the particles that made up the compounds. They were encouraged to use our class discussion board on Schoology to share ideas and critique fellow classmates. The lab design required outside research (using their iPads) and students could inquire about whether or not certain lab equipment was available in our classroom.
On the day of the experiment, students submitted a typed copy of their experimental design, which included a summary of what they intended to do and why they intended to do it. Their plan required a step-by-step procedure that they intended to follow, a list of materials/devices, and appropriate data tables. After conducting their lab, they submitted a post-lab discussion that expected them to make connections between their collected data and the strength of attractions between the particles in each compound.
Although each student devised a unique lab de
|Prepping capillary tube with compound|
sign, many students used Vernier probes to test the conductivity level of each compound upon being dissolved in water. Through research, several students learned about Mel-Temp devices and asked if we could obtain this piece of equipment for our classroom. Most high schools will not have this device (although a hot water bath could be used to determine melting points that are less than 100 degrees Celsius.) Luckily I found two universities that were willing to let me borrow some Mel-Temp devices for this lab. My students were excited about the opportunity to work with real chemistry instrumentation. (Although I admit, I was more giddy than they were!)
What did I learn from this experience? The ability to design and conduct an experiment varied greatly among students. Some students stood out as rock stars and embraced their first chance at freedom in the lab. Afterward I had one of my female students tell me that “This was the best lab we’ve done all year.” When I asked her why, she told me that she loved having the ability to control the experiment and make her own decisions. Another student told me
|Testing the conductivity of a solution|
afterward “I think I want to be a scientist.” That comment alone was enough to convince me that my students needed more experiences like this one. On the other hand, one student looked confused as the lab started and told me “I have no idea what I’m doing.” He had failed to collaborate on the discussion board and never created a procedure. This student typically receives “A” grades on assessments in my class. It helped me recognize the difference between students who could memorize content versus apply content to solve a problem. Clearly this student lacked the ability to apply his knowledge.
On a final note, students were randomly given two different white compounds to analyze. (I used five different compounds labeled A-E and assigned each student two different letters.) They did not work with assigned lab partners, but they were allowed to collaborate with classmates during the experiment. Students did not receive input from me on their procedure before the lab started. As a result, some students realized afterward that they collected too little data, and other students realized the results of certain tests provided useless data.