Study Chemistry

Inspired by the going-ons in your lab section, you turn to your chemistry textbook, taking a crack at the problems. There is, you think to yourself, not too much to worry about here.

The textbook problems turn out to be easy enough, with most of the concepts being one that you were already at least somewhat familiar with. At the end, you’re left with a few of the mathier problems that that you’re not totally comfortable with (why does everything seem to require a ton of math?). They’re not completely out of your reach, so within an hour or two, you think you’ve got a pretty respectable attempt at the homework down.

Now comes the real challenge—Professor Styles has a set of hand-written problem that she’s come up with herself, which as she says, are “designed to make your mind bend in uncomfortable ways.”

The first problem is titled “A High-School Review.” You look through the problem:

A closed 600.0 mL flask contains solid mercuric oxide and air initially at 21.0 ⁰C and 101.3 kPa. When heated, mercuric oxide decomposes completely according to the reaction:
2 HgO(s) → 2 Hg(s) + O2(g) 
After heating, the flask is at a temperature of 75.2 ⁰C and has a pressure of 205.5 kPa. What mass of mercury metal is in the flask when the reaction is complete?

Seems straightforward enough, you think—just basic stoichiometry. You just need to calculate how much many moles of oxygen there are in the flask after the reaction (and the Ideal Gas Law will give you that; this is high school review after all), and the number of moles of mercury produced kinda just falls out from the equation…

You put your pen down on paper, about to scrawl out the solution, when you pause. There’s an obvious thing that you’re missing, and you’re kinda pissed at yourself for not getting it earlier. There’s going to be air in the system before the reaction takes place, so you’ve got to take that into account when calculating the amount of oxygen produced!

But with that in mind, the calculations go smoothly, and with a little help from your calculator, the right answer gets spit out in the end: 7.11 grams. All told, that was simple enough. Not exactly “mind-bending,” so you look to the next problem to see if it has anything trickier…

At some point, you look up and catch the time. Past midnight already? Well damn, it’s roundabout time to sleep!