This week in AP Chem, we focused
on stoichiometry. On Monday, we turned in our first lab report of the year done
on carbon copies. Being in the Health and Medicine magnet, I was very familiar
with using lab journals; we use them everyday in health and med. During the
first half of the week (Monday and Tuesday), we reviewed the stoichiometry we
had been practicing ever since the first day of school. We completed problems
dealing with a certain amount of an atom/compound reacting with another
atom/compound in excess, and creating a product.
This week I was very happy with
my progress regarding stoichiometry. I was having a lot of trouble last week
with these kinds of problems because I kept insisting on using proportions;
they may have worked, but they don’t do a very good job of organizing my units.
However, one day I sat down and did stoich problems over and over again by
following the lectures online, and after one specific problem, I suddenly
understood the method by which I should solve these problems. I now use the
“times and a line” method whenever I am solving these kinds of problems. I now
realize how great of an organizing tool the actual process is. Although the
mole to mass and mass to mole conversion can be tedious along with writing the
actual name of the molecule next to it, the process has really helped me cancel
out my units and get the correct answer. Because I finally understand it, I
really like doing stoichiometry problems now!
Later on in the week we made stoichiometry a little more complicated.
We actually started limiting the reactants instead of having an excess of the
other reactant. In order to find the limiting reactant (the reactant that
produces less of the final product), we found the amount of product that would
come out of each given amount of reactant. The reactant that came up with less
of the product would be the limiting reactant. Now that I finally understood
the stoichiometry process, limiting reactants was not too challenging for me.
Calculating yield of a reaction was also quite easy, it was
a simple matter of finding how much of the product was actually made versus the
amount we calculated. The equation was: (actual yield)/(theoretical yield) x
100 = percent yield.
We also worked on particle diagrams before and after a
reaction. We were given a jar in which we had to draw the correct distribution
of molecules derived from the chemical formula (after balancing it). What I had
to wrap my mind around was that the jar wasn’t opened during the reaction, so
the same molecules are still there, they’re just arranged in different
molecules. I had to remember to draw the excess left from the reaction
also.
We whiteboarded the particle diagrams, just as we had been
doing with the various stoichiometry problems earlier in the week. I realized
how much whiteboarding helps me understand a concept. By viewing the thought
process another student/table group took to solve a problem, I was able to
compare it to my own and even adapt it, sometimes. If a mistake was made, we
all went over it as a class so we would avoid making that mistake in the future.
While whiteboarding, it’s okay to make mistakes.
By the end of the week, we started with empirical formulas.
So far, I’m still somewhat new to the concept, but as I complete more problems,
I’m starting to get the hang of it. Calculating the empirical formula using the
percent composition of elements is somewhat daunting, but given enough
practice, I know I can conquer those kinds of problems, also.
Overall, I’m very happy with my progress in stoichiometry
this week. It has been a very rewarding learning process and I’m already
surprised with the relative ease I feel with stoichiometry now. I am nervous
for next week’s test, but I will practice and study everything we have done
these past few weeks to ensure that I succeed!
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