Last week Chemistry conducted our first laboratory exercise. The laboratory exercise centered around the newly-learned concept of density.
On Monday, we learned how to represent large and small numbers in scientific notation, and then the remainder of the week was devoted to density.
On Tuesday, we learned the concept of density, and then participated in a discovery activity where we used graduated cylinders, rulers, and electronic balances to determine the density of a liquid (water) and a solid (aluminum in foil form). For water, we measured the volume and the mass of water, and then (this will make the students cringe if you say it to them) “plugged and chugged” those values to find density using the following equation: 
. Where d is density in either g/mL or g/cm^3, m is the mass in grams, and v is the volume in mL or cm^3.
Aluminum foil was a little bit more tricky. They were given the density of aluminum foil in strange units: 0.098 lb/in^3. They then had to use the previous week’s skill of dimensional analysis to convert those units to g/cm^3. While this was tricky, it was within their capabilities since we had completed at least one warm up in class where we converted double-units in this form. Those students in Algebra II are also getting a double-dose of dimensional analysis, since they are practicing the skill in math class.
This provided students with an authentic use of the previously-unknown Dimensional Analysis.
From the conversion of aluminum’s density into usable units, and their measurement of the length and width of a rectangle of aluminum foil, students were then able to calculate the thickness of aluminum foil. They were asked to do this for two different rectangles, cut from the same roll of aluminum foil. Surprisingly, the thickness values were different for the two rectangles. How could that have happened? Students were asked to speculate different reasons for this inconsistency.
After we’d practiced with finding density, we then used density as an analytical tool to identify the metal present in paper clips and in the core of pennies. For both of these procedures, students were asked to write their own procedure. Since they had practice both massing and finding the volume of items from the previous activity, the real test of the procedure writing was to craft a procedure that was descriptive enough to be repeatable by any scientist, based solely upon reading.
Once the density had been acquired, students then had to check that density against all the known densities of metals to identify the metal in question for each of the objects. Once that was accomplished, the students had to analyze their data for precision and possible sources of error. The second part of the Using Density lab, the part that asks for the metal at the core of a penny, will become the students’ first Formal Lab Report.
In order to help students write the best report possible, we spent Friday with our weekly Friday Quiz, and then analyzed a previous lab report with the sharp eye that I will use to grade theirs. Hopefully through recognizing mistakes in an other student’s work, and seeing the criteria I will use to grade their lab reports, students will be aware of the common mistakes and consciously avoid them.
The Friday Quizzes were graded on the spot and returned to the students on Friday, so that they could use their quizzes to study for their Monday test. Test questions look similar to, if not identical to, the quiz questions from their Friday Quizzes. As such, Friday Quizzes serve as more than benchmarks of understanding; they double as study guides.
In Science/Math studying, which is different than studying for a humanities class, it is important to actively rework problems. Both science and math are testing a process, which cannot be practiced by reading, alone. I can tell in my preliminary grading of the test, who has and who has not studied by practicing the questions on their quizzes. If students, in studying for Chemistry, make corrections to their quizzes, and practice the questions on their quizzes, then they will do well on tests and on the ultimate Chemistry EOC. My quiz questions – turned – test questions are at the same level of difficulty as those that students will see on the EOC. Performance on my tests is an indicator of performance on the EOC. If students study properly for the test (correcting problems and reworking problems from their quizzes), then they will do well on the tests and in turn on the EOC.
On that note, if you wish to do something at home that will help your students succeed, they could use some guidance. The Chemistry/Algebra II combination is usually the first time that they are asked to do, what a metacognician named Bloom calls, analysis-based thinking. Put simply, they need to be able to reproduce a process, rather than a fact. This is difficult for students, as school up until this point has trained them to be able to recall facts, rather than processes. They are no doubt feeling overwhelmed by having to juggle a lot of balls in the air: proper mathematical operations, correct units, correct number of significant figures, starting with the correct value (as there are often more than one number in a chemistry word problem), ending in the correct units, properly entering all values into their calculator, properly recording the calculator output on their papers, remembering to add the correct units, remembering to show all of their work, and … My head would be spinning, too, had I not had years of practice in the field. I’m sure that they could use a hug and any guidance you can offer on how to manage a lot of small details. And as parents, you are the best detail managers around.
A lot of the work that students have submitted is partially complete in the sense that they are juggling, but dropping a few balls. The “balls” most often dropped: showing all mathematical work, and putting units on final values.
