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The familiar Z shape used by Mrs. Rathbun in the classroom to illustrate chemistry problems involving stoichiometry have now returned to haunt (or help) us as our study of chemistry shifts its focus from Lewis structures and VSEPR theory to acid/base reactions involving molarity equations. These new problems oddly combine the concept of molarity and the previous concept of stoichiometry in a dizzying, mind-numbing problem that serves the sole purpose of relating the volume of one substance (substance A) to the volume of another substance (substance B) by using their specific molarity and the balanced chemical equation. Tackling this type of a problem requires three, main steps, though sometimes it requires more if the original information given is in the wrong format or if the final answer is requested in an odd, unusual format. Generally, however, this is a three-step problem, and Mrs. Rathbun, knowing that us students may easily get lost in the many steps, always draws a big “Z” on the class notes, placing the information that we’ve been given about substance A on the tip of the upper, left-hand horizontal bar and the unit requested by the problem for substance B on the tip of the lower, right-hand horizontal bar, leaving the junctions between the horizontals and the slanting bar blank for now. Next, she writes the abbreviation “BCE,” which stands for “balanced chemical equation,” on the slanting bar. Now we can visually see where we need to go and how to go about getting there.

 

This Z figure used to complete these types of problems is the brunt of many jokes in chemistry class. Because it resembles the classic “Z” mark made by the fictional outlaw of Johnson McCulley’s original story, “The Curse of Capistrano,” known simply as Zorro, we always get a kick out of using the Z in class. Who would’ve ever guessed that this trademark of the Zorro series would now be snatched from the world of dramatization and turned into an educational tool for studying the application of molarity and stoichiometry in a chemistry problem? Anyway, we’re grateful to McCulley’s creativity with this character, since using the Z figure is extremely helpful in keeping your wits about you when you’re in the middle of this type of problem.

 

When Mrs. Rathbun asks us why we know something is correct in one of these types of problems, a common reply garnering many chuckles from both the students and Mrs. Rathbun is “because the Z, it tells me so.” Proceeding through the problem, Mrs. Rathbun exhorts us--again to loud, rapturous laughter--to “use the Z, Luke.” Okay, you might be thinking right about now that our chemistry class is primarily made up of jokes, funny little learning aids, and maybe a few tests and homework assignments on the side. Though very true about the jokes and funny learning aids, those tests and homework assignments are definitely not just a side-dish that we peck at like a disinterested child with the promise of desert nagging at him incessantly. No, though our class is tons of fun, we do eventually have to break up the party and get down to work, practicing our skills with the Z and with molarity problems.

 

Finding our places at the virtual starting line at the tip of the upper left-hand horizontal bar of the Z, we take our stances, waiting for the signal. As the gun fires, exploding with a furry of noise and power, the race through the Z maze begins, and all chemists scramble in a maddening sprint from the left-hand top horizontal bar to the right, completing their molarity conversion from liters of substance A to moles of substance A. With the mock competition fiercer than ever, we now slide down the slanting bar from the top right-hand corner to the lower left-hand corner, using the balanced chemical equation (BCE) to equate moles of substance A to moles of substance B. And now, that illusive finish line looms eerily in the dark distance before us, shrouded by not so much mist as before, and we put on extra force, lurching forward from the lower left-hand horizontal bar to the right, completing the conversion of moles of substance B to liters of substance B. Elated by our achievement, we pat each other on the back as our practice run comes to a sudden, abrupt halt, breathing hard from the mathematical sprint we've just completed.

 

Though definitely a ton of work to complete, these problems are also a lot of fun to work. As the saying goes, “nothing ventured, nothing gained,” and I guess it’s true in this case as it really is the complexity of these problems that makes them so rewarding. Also, because they stretch our abilities to comprehend and apply what we’ve learned, they tie together many other concepts taught previously in chemistry class. Experiment 10.2, for example, revolved around one such problem that really helped in tying the concepts of acid/base reactions, stoichiometry, molar mass, and molarity all together under the grand Z that we used to deduce the final conclusion of the report. But for now, following the setting sun, Zorro the masked chemist rides onward to another, grand adventure, as we, too, will in the coming month as we delve into the complexity of solution chemistry and the gas laws.

 

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HS Chemistry English 8, section 5 HS Chemistry, Section 2 JH Latin 2