Titrations and Microscale Chemistry

What are we doing to help kids achieve?

     I tend to enjoy acid base titrations for several reasons.  First, students get to work with burettes, acids, bases and they see a nice "color change" when they reach an endpoint. Many times, students who tend to struggle with pen and paper testing excel at the "hands-on" approach. Titrations also dovetail well with stoichiometry which provides a nice review of information closer to the end of the year.

     This year in one of my classes we just did not have the chance to set up the burettes, standardized the base and find the concentration of the unknown acid. Instead, we went to "plan B". Everything was changed to microscale. Students first started titrating 1 M HCl with 1 M NaOH. Each time they just "counted drops" and because it was microscale they did multiple trials while checking multiple indicators to see which was the best.  Next, they had to solve for the concentration of the unknown HCl solution. I did a simple dilution on some of the bottles and just placed blue painters tape over the old labels. The unknown took just a few minutes to create.  Students could easily do multiple trials in a small amount of time. They also were able to count the drops required to form 1 mL of fluid and this lead to conversion factors. There was no broken glassware.

We also had time to add a titration. This involved solving for the percent of vinegar in acetic acid and then checking with the USDA's requirements for mustard and comparing answers. Most students were successful with the experiments. It also lead to allowing students to run their own experiments with less use of chemicals.

    Should this always be the way to go? Probably not. Students who are going on in chemistry probably should have the exposure with burettes. Should a teacher feel "bad" or "guilty" if he or she does not get to the burettes? That depends...are we teaching the students to be chemists or to think like chemists? I would suggest the latter. Both large scale and microscale have advantages and drawbacks. In an ideal world it would be great to always be able to put the experiments in the hands of the students with the best equipment possible...but if for whatever reason we can't, there is no shame in going to "plan B". Have you found a "plan B" that works better than you thought?  Don't be afraid to share...I would love to hear about it and I would bet so would others.  As an aside, most students had a 5% error when solving for the amount of vinegar in mustard just by counting the drops.......

Editor Note - In response to a request by a reader, Chad posted a worksheet for the Mustard Titration. You can find it  in the Supporting Information or in the comments. (6/3/19)