Given the current COVID-19, I’ve decided to make this lesson fully online. I’ve highlighted some of logistical questions that came to mind based on the design and how an online high school class would look like.
This activity goes over acids and bases and attempts to use LfU with SKI supports. It also tries to model scientific inquiry through PEOE (predict, explain, observe, explain) and how scientists engage in critiques while targeting misconceptions.
Step 1: Motivation through PEOE
Predict the products and observations for the reaction when concentrated aqueous sulfuric acid is poured onto solid sodium chloride (Barke et al, 2009). Explain your thinking by using a molecular diagram. State any assumptions you make about the reaction conditions.
H2SO4 (aq) + NaCl (s) → ?
We aren’t expecting students to come up with a “perfect” answer here, but many might immediately treat this as a double displacement reaction. They might experience disequilibrium when they realize that the states of matter are not both aqueous. Some may conclude no reaction occurs when using their solubility table.
We don’t necessarily expect them to recognize how the sulfuric acid behaves with chloride ion and if they apply the Bronsted Lowry theory. Some of this may also depend on the specific reaction conditions.
Step 2: Knowledge construction by showing an answer, reflecting on the prediction, and trying to explain that answer
In one experiment, the reaction was shown to produce gaseous hydrogen chloride:
H2SO4 (aq) + NaCl (s) → HCl (g) + NaHSO4 (s)
In groups, compare your initial answers from Step 1 to Step 2:
- Were you surprised by this answer?
- Why is it that a reaction did occur in this case?
As a group, design a possible set up for the experiment that would be able to capture gaseous hydrogen chloride and how you would know that hydrogen chloride was produced.
- Draw your lab set up (you can do this by hand and then upload a picture, or use online software like Chemix)
- Create a molecular diagram to show what is occurring during the reaction
- Justify your lab set up and explain how you would expect the reaction to proceed in the set up
- How can you test the identity of the gas?
A question that came to mind for this section was how students would work together and what the domains of an online class would be. Do students go to each class as per their rotary timetable? How long is each class? In this current situation, it’s more likely that your high school classes are in the same timezone, so this is a bit easier to work within. Steps 1 and 2 could be synchronous for the whole class or asynchronous. There may also be synchronous drop-ins available through conferencing software (e.g., Google Meet, Microsoft Teams, Bb Collaborate, depending on what is available).
In terms of the chemistry, I want students explore how this answer may have been created and how that data was collected. Since this may have been an unexpected answer, I also want them to explore and explain what’s happening at the molecular level to see how students’ mental models are developing (Barke et al, 2009). It would be good for the teacher to check in with students to compare their predictions and new answers. It’s possible that students made assumptions about the reaction conditions that cause their answers to be different.
Step 3: Further knowledge construction and refinement through a synchronous class discussion
The synchronous class discussion would take place through video conferencing software where students get to view other groups’ designs and ideas. Before the session, groups should post their designs with a brief summary of their ideas in discussion forum.
In the live discussion, groups will explain their design and why they think it works. Peers will be able to provide feedback and ask questions.
Depending on your class, you might also record the class discussion and upload. You would need the class’ permission for this. The idea here is that students who may have been unable to attend the synchronous discussion will be able to watch later on. The sharing through the discussion forum also allows for asynchronous participation.
Through this discussion, we’re interested in seeing if groups suggest using an indicator (e.g., litmus, pH paper) on the gaseous hydrogen chloride. The teacher should also probe students into discussing acids and acid theory (Bronsted Lowry).
Step 4: Watch a video of a set up for the reaction
Some possible videos:
Depending on the video, the teacher might highlight the observations as needed. This should be connected to the previous discussion in Step 3. They should also correct any mistakes that are made in the video, if any.
It’s helpful for students to see a live demonstration and see what the observations were expected to be. This part could be synchronous or asynchronous.
The teacher could also show their own set up an experiment and comment on what the observations would be. A set up and the expected observations are included in Barke et al (2009). From the molecular diagrams that students drew, the teacher can pick one that was correct and/or explicitly model the expectations. This is important in getting students how to visualize and problem solve schematically as per the discipline (Edens & Potter, 2008). The teacher should explain what’s happening with the solvent interactions and how the Bronsted Lowry theory is applied to come up with the answer.
Step 5: Motivate by comparison gaseous hydrogen chloride and aqueous hydrochloric acid
In the set ups you created and in the examples we say, the pH was always taken on aqueous hydrochloric acid. In the cases where indicator was used over the stream of hydrogen chloride gas, the indicator paper was wet.
Why is this step done? Draw molecular diagrams for gaseous hydrogen chloride and aqueous hydrochloric acid.
This is the second LfU cycle. It lives within the larger anchored example, that served to motivate students with an unexpected and interesting reaction. It’s important for students to recognize that gaseous hydrogen chloride is made of molecules while an aqueous hydrochloric acid solution contains ions.
Step 6: Knowledge construction and refinement by exploring a PhET simulation
Using this acid base solution PhET simulation, examine the differences between:
- acids vs. bases
- strength
- concentration
- pH
Pick one solution of your choice. Note its concentration and pH. Change the view to graph. Create a concentration vs. species graph using a linear scale. What do you notice? Why does the PhET choose to use a logarithmic scale?
Come up with conclusions for each of the following:
- Why do aqueous acids and bases conduct electricity?
- If a strong acid and a weak acid have the same concentration, how do their pH and conductivity compare and why?
- If a strong base and a weak base have the same concentration, how do their pH and conductivity compare and why?
- If a strong acid and a strong base have the same concentration, how do their pH and conductivity compare and why?
- Is a concentrated base the same as a strong base? Why or why not?
- Draw molecular diagrams for hydrogen chloride gas, concentrated hydrochloric acid, and diluted hydrochloric acid. Include a caption for each image to highlight their features.
- Solution X and Y both have similar conductivity and pH. If one solution is a dilute strong acid and the other is a concentrated weak acid, how would you distinguish between the two?
After a lot of internal conflict about this particular PhET, I started to see that it was intended to scaffold student learning and some of the visualization choices were done for simplicity. The simplicity creates productive constraints for students to work within and develop their mental models through interaction (Finkelstein et al, 2005; PhET Simulations, 2013). Being able to interact with each variable and see the effects also supports embodied learning (Niebert et al, 2012). By reading Burke et al’s (2009) recommendations on teaching acids and bases, it’s better for students to develop an understanding of acid base behaviour through a static model before they examine dynamic equilibrium. When the students work on the PhET, it might be helpful to explicitly tell them that they are looking at snapshots of what’s happening at the molecular level. Drawing attention to what’s not shown by the PhET (e.g., solvent interactions, dynamic equilibrium) would be helpful in starting the next LfU cycle.
References
Barke, H., Hazari, A., Yitbarek, S., & SpringerLink ebooks – Chemistry and Materials Science. (2009;2008;). Misconceptions in chemistry: Addressing perceptions in chemical education (1. Aufl. ed.). Berlin: Springer. doi:10.1007/978-3-540-70989-3
Edens, K., & Potter, E. (2008). How students “unpack” the structure of a word problem: Graphic representations and problem solving. School Science and Mathematics, 108(5), 184-196.
Finkelstein, N.D., Perkins, K.K., Adams, W., Kohl, P., & Podolefsky, N. (2005). When learning about the real world is better done virtually: A study of substituting computer simulations for laboratory equipment. Physics Education Research,1(1), 1-8.
Niebert, K., Marsch, S., & Treagust, D. F. (2012). Understanding needs embodiment: A theory‐guided reanalysis of the role of metaphors and analogies in understanding science. Science Education, 96(5), 849-877. doi: 10.1002/sce.21026
[PhET Simulations]. (2013, Jan 12). PhET: Research and Development [Video file]. Retrieved from https://youtu.be/qdeHagIeyrc