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Titration Experimentation

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It’s rare for Seattle to have beautiful weather, but this week has been gorgeous. What better way to spend all of class outside, than to measure titrate unknown acids?? ***

I’m generally of the mind that kids can do a lot more than what people allow them to do. It’s why my husband and I are teaching our nearly-3-year-old to chop vegetables with a kitchen knife (supervised, of course), and really like Gever Tulley‘s ideas.

So when one of my students, who has a penchant for performing his own experiments, found an old bottle of muriatic acid in a dark corner of a barn (I didn’t ask), and he asked what the label meant by “35%” strength, I figured it was actually an opportunity.

Having just gone through a unit on acids and bases, we went through the whole shebang of performing titrations: neutralization, choosing appropriate reactants, balancing equations, titration procedures, using indicators, calculating molarities, and (of course) safety measures. Students here aren’t often trusted with the one nice, glass buret (which I think is ridiculous, and, frankly, I didn’t trust plastic for this particular titration).

So after performing a more controlled titration on Tuesday, my students decided that this new titration should be done outside, on a lab table, upwind, and with limited amounts of acid. I approved their procedure, including choices of base and indicator, and they impressed me with their careful handling of materials and glassware and chemicals, as well as careful measurements and each taking a turn with the pipette and buret (even the extra-timid student!). All three trials lead to pretty tight data. Their assignment is to calculate the acid molarity for each trial, and give an average.

In addition to this awesomeness, the neutralization produced a visible precipitate, so they wanted to crystallize it to see if it has the properties (thank you, introduction to the CRC Handbook!) of the predicted salt. I might even throw some stoich/limiting reagents in there to see how much salt should have been generated. For the record, I’ve no idea if crystallizing will work, or if the indicator or impurities will get in the way or something.

For me, this is the best day of the year so far: we covered all of the year’s major “chemistry” topics in about 75 minutes, and it was mostly student-generated. Even better, we’ll have another day (at least!) with more of their questions and ideas.

*** Important note: I don’t generally blog about my current students. Teaching individually means that people could potentially identify them very easily/quickly, and I don’t want that problem. Today, however, my class really, really impressed me!


One response »

  1. Pingback: Thinking Is Hard (When You Tell Me What to Do) | wwndtd

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