Lab #8: Mole Baggie Lab

Summary (Purpose)
    The purpose of this lab was to allow students to apply the concepts of moles and molecular mass. The lab also allowed students to deepen their understanding of these two concepts as well as to explore the relationships existing between them by asking students to find a correlation between their unknown substances and the theoretical molecular mass of the possible compounds.
     During the lab, students were given two plastic baggies, each containing an unknown substance. Each bag also had a a sticker telling the student the mass of the baggie as well as one other piece of information: Bag A revealed the number of moles contained in the bag while Bag B informed the student of the number of particles (in this case, molecules or formula units) contained in the bag.

Summary (Process) 
     Before we began massing we first decided to find the molar mass for each possible compound; this way we could compare the molecular mass of the substance with that of the possible compounds and thus identify which formula the substance had. This was done by writing out the chemical formula of each possible compound and then adding up the average weighted atomic mass for each compound, which yielded the molar mass of each compound in turn.
   Next we began our calculations, starting with Bag A6. First, we massed the bag and subtracted the given mass of the bag itself in order to find the mass of the substance. We set up an equation using what we knew; since
                 Molar Mass= # of grams in sample/# of moles in the sample,
  we rearranged the variables and produced the equation
                # of grams in the sample/ molar mass= # of moles in the sample.
Thus, after substituting in known values and  solving for the molar mass, we found that the molar mass of this substance was 142.22 g. We then concluded that the substance was sodium sulfate due to its molar mass, which was predicted to be at 142.0431 grams.

For the second baggie we went through a similar process, only this time we had to convert the raw number of particles into moles before inserting the value into the equation. Like the first bag we massed the bag, subtracted the mass of the baggie, and then, after substituting in known values, solved for the molar mass. Our result this time was 97.427 gram, which we found to be close to the molar mass of calcium carbonate--100.087 grams.

Bag Identities 
Bag A6 is sodium sulfate.
Bag B5 is calcium carbonate.