Content Design

I had three main goals in mind when designing the content for my new lab for College Chemistry 1: bring real world examples into the classroom, generate high student engagement with the lab, and connect the lab material to the course curriculum.

I began by conducting literature review on student engagement and ways of bringing real world examples into the chemistry curriculum. My literature review is summarized on this page. For the "real-world" portion, I focused mainly on looking for ways that others used environmental samples in chemistry labs. I found several examples of full semester chemistry curriculums designed around environmental chemistry including Chemistry in Context from the American Chemical Society and the Chem Connections Project developed by the University of California at Berkley and Beloit College. For my new lab, I decided to adapt one of the labs from the Chemistry in Context 4th ed. Lab Manual.

My learning goals for students who performed the new lab were as follows:

Students will measure chloride in water samples by titrating with silver nitrate
1. Students will perform a titration using burettes
2. Students will use a colorimetric indicator solution
3. Students will use titration results to calculate chloride concentrations
Students will identify sources of chloride in local water bodies, wastewater, and drinking water
1. Students will relate their titration results to local sources of chloride
2. Students will compare and contrast the amount of chloride and sources of chloride for different water sources

Dr. Smith and I chose this lab because titration was a good lab skill to add to the curriculum and chloride in water is an easy topic to connect to the local community. Downtown Madison is located on a thin strip of land between 2 lakes, so water quality is a topic that all residents are frequently exposed to. Road salt and water softeners are some of the main sources of chloride, and both of these things are frequently used in Madison. The local wastewater treatment plant has an ongoing project of reducing chloride output from the plant. There are also many agricultural sources of chloride, which the students from rural areas showed more interest in. The water samples we decided to use included tap water (sourced from groundwater), Lake Mendota Water (collected in downtown Madison), and wastewater treatment effluent. I collected all of the water samples ahead of time and brought them to the lab. If the lab is taught in the future, we considered offering students the opportunity to collect their own water samples to bring in and analyze.

One of the challenges of the designing the lab was figuring out how to get enough replicates of the data so that the students could see significant differences between the samples, but also make sure all of the students could complete the lab during the allotted amount of time. We decided that each pair of students would only work with one water sample and would conduct their titration in triplicate. After finishing the titrations, each group entered their results into a class spreadsheet that was then posted on the course website for all students to use in their data analysis.

You can see the lab write up that was handed out to students here. The pre-lab exercise consists of a short reading on environmental sources of chloride that I adapted from an Illinois State Water Survey Report followed by several questions asking about the importance of monitoring chloride and predictions about the water samples to be analyzed in the lab. The handout includes detailed instructions for the data analysis, which fit in well with the concurrent lecture material about molarity calculations. I designed the discussion questions to cover range of levels of understanding - from simply reporting what they found in the data analysis, to predicting what would happen if they analyzed samples from different sources or changed part of the titration method.

In general, student grades on the lab were high, and answers to the pre and post lab questions indicated good understanding of the material. 31/33 students wrote a well explained hypothesis about which water samples would have the highest and lowest concentration and 31/33 were able to effectively write about comparing their results with their hypothesis. Greater than 90% of students correctly used their titration data to calculate the concentration of chloride in each sample. Additionally, Responses to post-lab question four show that most students had a good understanding of how solubility rules were important to the titration method; 76% of students were able to identify that NaNO3 would not be an acceptable replacement for AgNO3 in the titration because the sodium ion will not react with the chloride and chromate ions to form the precipitates necessary to determine the endpoint. An additional 15% of students demonstrated at least a partial understanding of this difficult question. Common mistakes in the lab reports include not averaging the data correctly and not using significant figures in the calculations.

While the lab was generally good, there were a few changes I recommended for teaching the lab in the future. The pre-lab reading should be edited to include more emphasis on water softeners and the fact that wastewater treatment does NOT remove chloride. Several students wrote the opposite in their hypotheses. In the procedure, more information should be given about specific details that students should write down in their lab notebooks – for example, which water sample they were assigned and a description of the color of the water sample before and after the titration. The data analysis and post lab sections should be combined, and there should be a clear outline given for how the data should be averaged. Students should be reminded to use sig figs and to show their work, even if the calculations are done in a spreadsheet. While these additional details may not be necessary to include in a lab for a more advanced class, College Chemistry 1 students tend to have little lab experience in a similar setting, and this lab exercise took place near the beginning of the semester. The more detailed instructions should lead to lab reports that are more structured so it is easier to assess student knowledge.

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