In honor of the International Year of the Periodic Table: A familiarity with the chemistry of some of the elements more commonly encountered in everyday life is a valuable learning experience for all students. Oxygen is the second in this series of elements to be discussed as part of the Element of the Month program. #IYPT
Students can build their own Hoffman apparatus. An animation of the electrolysis on a particulate level is available to show students before, during or after students perform the electrolysis.
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.