Embracing the idea that students already create an image, create an idea, of what is happening when they observe a demonstration, lab or activity. The goal is to have the students make that model more concrete through drawing it.
Curricular Alignment for Student Success
The February 2018 issue of the Journal of Chemical Education is now available online to subscribers. Topics featured in this issue include: diversity within the classroom; assessment and curricular alignment; innovations in laboratory curriculum; electrochemistry; analytical chemistry labs; exploring materials science; engaging teaching approaches; historical perspectives; distilling the archives: lab-on-a-chip and microfluidic devices.
Chad Hustings blogged this past school year about building his own Hoffman apparatus for each group of students. I have been using a Hoffman apparatus that had been purchased by my district before I began teaching there over 20 years ago to demonstrate electrolysis of water, but providing each student group with the ability to perform an electrolysis themselves is a powerful activity. I have used a different version of a homemade Hoffman apparatus, but after reading Chad's blog post, I decided to use a version close to his.
If the Hoffman apparatus is built ahead of time (this takes about 5 minutes for each one if the teacher builds them), then the activity and discussion should take less than a 45 minute period.
There are many places online to build a DIY Hoffman apparatus. The ACS offers an electrolysis of water lesson that includes a hand made Hoffman apparatus(link is external) as part of a unit on energy that I used as a resource.
Electrolysis of an aluminum nitrate solution produces oxygen at the anode and hydrogen at the cathode.
Electrolysis of a potassium nitrate solution produces oxygen at the anode and hydrogen at the cathode.
Electrolysis of a calcium nitrate solution produces oxygen at the anode and hydrogen at the cathode.
An electric current is passed through a sulfuric acid solution. Gases collected at the electrodes are tested.
Electrolysis of a cobalt(II) nitrate solution produces oxygen at the anode, and hydrogen and cobalt at the cathode.