For Day 84, we continued our discussion of counting by weighing with a relative mass activity adapted from the AMTA modeling materials. In this activity, students massed pill bottles full of paperclips, nickel shot and pennies (basically whatever I could scrounge up that I had at least 25/bottle of).
Student then completed a series of calculations converting between number of items and mass of items. Finally, students calculated the relative masses of each item and related them to elements on the periodic table. We then whiteboarded and discussed the practice of counting by massing and relative mass.
I gave my students once last challenge before introducing the mole; the bean challenge. For this challenge, I told students that each single-bean bottle contained 50 beans but the mixed bottle contained an unknown number of bean compounds. A bean compound consisted of 2 white beans and 1 red bean. I challenged my students to figure out how many bean compounds were in the mixed bottle.
This challenge makes it really easy for students to make the leap to adding molar masses of individual elements to figure out the molar mass of compounds later on.