I’m trying out a new PBL I developed in my chemistry 12 class, along with a colleague. The problem is as follows:

5 solutions are given to each group. The identities of the solutions are given, but they need to figure out which bottle is which chemical. In order to make sure there is good variety of skills involved in solving the problem (i.e. can’t just use a bunch of indicators for the whole thing), a couple of restrictions are put into place:

Only allowed 2 types of indicators. No universal indicator provided. Data needs to include a graphical component.

The hope is that number 2 gets students thinking about titration curves.

Assessment

The assessment is fairly straight forward:

The idea is the PBL will get students thinking about how to identify the required chemistry such as calculating out the pH of weak acids/bases, and they will ask me questions on how to do it (after they’ve tried for themselves).

One of the biggest issues with PBLs like these is that if every group gets the same solutions, it’ll reduce the amount of thinking involved. Students tend to copy or play follow the leader without a lot of consideration as to why they’re doing it. Another long term issue is if the same PBL is conducted over multiple years, students generally have an easier time doing it presumably because they’ve been told my past students. To address these problems, this PBL has been “modularized“. I’ve created a set of solutions I can mix and match to control the difficulty of the process (I would tailor this to the strength of the group) and make sure everyone in the class has variety or something unique. This would also ensure the PBL doesn’t get stale over a longer period of time.

The list of solutions and some possible combinations are:

[EDIT: The combinations have been removed, but if you are interested fire me a message!]

Update

For the next iteration of this PBL, I would consider adding phosphoric acid to the list – we didn’t have any so we had to adapt!

The second thing I would consider is limiting students to 1 indicator of their choice – one group was able to differentiate all the solutions using 2 indicators. I want to force them to perform titrations (and analyze graphs).