There is a traditional stoichiometry lab I have done before. It involves adding dilute hydrochloric acid to sodium bicarbonate, boiling off the fluid and then getting the mass of the sodium chloride. Students then can solve the percent yield for the sodium chloride based on the amount of sodium bicarbonate they use. It is not a bad lab.Something about having hot ceramic watch glasses with acid just makes me a bit nervous.I am not sure where I got this new lab, but it has been one that has evolved over the years It is quick, dirty, relatively simple and uses over the counter (mostly) materials.
Are students reflecting on what their calculated values indicate? This question constantly runs through the minds of chemistry teachers across the country. Recently educators have seen shifts in instruction that promote connections to real-world phenomena using conceptual depth in understanding.
“So what corners of the periodic table do I have to memorize in order to get an A on the trends quiz?” This was a question that was asked by one of my students at the beginning of our periodicity unit. For countless educators we teach chemistry because we have a passion for trying to understand the world from an atomic level. However many of our students have extrinsic motivators which result in attempts to find shortcuts to recall the material. If we want to avoid responses like the one stated above we have to identify if we are asking thorough questions when assessing our students.
What am I doing to help kids achieve?
In an earlier post, I discuss some of my unit planning that (I hope!) further breaks down a few of these misconceptions - my students are not teaching themselves on google. They are weaving back and forth between learning content and the larger reason for learning the content.
However, every single one of these comments above are valid. It is really difficult work to ultimately balance individual accountability and group accountability. Every student needs to master basic stoichiometry before they leave my general chemistry course.
One challenge I have is knowing how to evaluate labs properly. In writing my new lab manual, I am setting up rubrics for each lab. The ultimate goal is for this manual to be used by all instructors across the chemistry department at our community college, so they need to have a consistent grading system. Writing these rubrics has been challenging.
First, I had my students examine the conductivity of a puddle of water the size of a nickel. They checked for conductivity. Then they took a very small amount of sodium carbonate and a fresh puddle of water and pushed in a few crystals from the side. You can still see the crystals in the water but it tested positive for conductivity. They had to explain this. They did the same with a fresh puddle of water and a few crystals of copper (II) sulfate. Again, it tested positive for conductivity but they could still see the blue crystal. Finally, they started again with another fresh puddle of water, pushed a few crystals of sodium carbonate on one side and on the opposite side they pushed in a few crystals of copper (II) sulfate. After waiting five minutes, a solid dull blue precipitate formed in the middle. Also, the drop tested positive for conductivity.