Sometimes it just all works out right. The timing of the lessons and the timing of a lab. This year, I introduced a simple new lab about activity series on the same day that I taught about predicting single displacement reactions. It was great. In one block period, the kids went from not knowing that single displacement reactions existed to predicting outcomes of reactions based on their own activity series. I felt that the learning was deeper and can’t wait to see how things progress! Here is how I did it.
Intro Single Displacement Reactions
I am sure many of you use a “chemical dance” metaphor through your reactions unit. So do I. The kids already understand the premise, as I have already taught synthesis and decomposition in the previous days. The problem with single displacement reactions is that not all of them work. We talk about the “reactivity” of metals being the loss of electrons. They don’t know the term oxidation yet, so I introduced it to them. But I spend most of my time just using the term “reactivity = losing electrons”. It is the first day, after all.
Do a simple demo
As I’m explaining single displacement reactions, I take a new shiny penny and put it in a 50 mL beaker with about 20 mL of 0.1 M silver nitrate. I asked the kids, “How would we know if a chemical reaction takes place?” Then I continue teaching while the penny slowly changes color and then eventually starts growing black, mossy silver. I leave it growing through the whole class and by the time they leave the penny isn’t even visible any more.
Connect the demo to an activity series
I use copper and silver nitrate as my example, and we discuss the activity of these two metals. Through discussion, we discover that copper is higher on the activity series than silver. Then I started an activity series on the board. The only thing that we know is that copper is higher than silver, somewhere.
Introduce the inquiry lab
But copper and silver aren’t the only metals we need to place on the activity series. Then I will introduce the inquiry lab. Their challenge is to place Mg, Zn, Pb, Cu and Ag on the series. Right now, all they know is that copper is above silver. I put them into their lab groups with a real simple lab form. They have to come up with a way to use a 24-well plate to complete all the reactions in order to build the activity series. I gave them 0.1 M nitrates of all the metals involved and then gave them small pieces of each of the metals except silver. I used small pieces of zinc from a sheet, segments of magnesium ribbon, copper pellets, and then drips from freshly melted lead.
Pro-tip: My lead sheet has been in the lab for eons. It is very oxidized. Before class, I lay out a sheet of aluminum foil and use a Bunsen burner to melt the lead and make small drips on the foil. Then you can peel off bright shiny lead drips that will fit in a 24-well plate. And if the drips are too big, just cut them in half with scissors. It makes it so much easier to see reactions on the lead.
Students write methods
Instead of telling the kids exactly what to do, I let them get in groups and decide what their methods will be. I give them two simple restrictions. You may only put one piece of metal in a well. You may only use a maximum of 1 mL of nitrate solution in a well. Kids sit and chatter for a bit, but eventually, every group figures out the reactions they need to do. I leave some scratch paper in the lab, so that students can label their 24-well plate. This is important so they remember what they did!
Complete the lab
Students then follow their own methods. It only takes about 15-20 minutes to get all of the wells filled and reacting. I only used one beaker of each solid and one flask of each nitrate solution. The students simply pass them around and take what they need. Once their plate is completed, I give them a five-minute bathroom break. This is to allow the magnesium and zinc nitrate to react. This reaction is minimal as they are near each other on the activity series. A few minutes of wait time is helpful. After break, the kids come back to the classroom where I explain how they are going to record their data on the sheet provided. And then I explain clean up. Since the lab includes lead ions, all waste goes into a receptacle with aluminum foil in the bottom to react it out.
Make the activity series
After cleaning up, the students gather with their lab partners in the classroom to analyze data and make their activity series. I was honestly shocked how little help grade-level chem students needed. Once they have their activity series, they write them on the board. I completed the lab three times this week. In two periods, all of the series were correct. In one class (you know that class… the special one) there were a couple groups who had switched Zn and Mg and one group who had the activity series upside down. We get to talk about that as a class to solidify understanding.
Once they have reported their activity series, I hand out the “official” one they will use on the test and they get to check their results. It is very satisfying to the kids to see that they were able to do “real science”. It’s a full 90-minute period, but the growth is amazing. This is a process that I will use every year from here on out.
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