A traditional hydrate lab used to demonstrate the formula of a hydrate is the dehydration of copper sulfate pentahydrate. Most use a Bunsen burner as a heat source. At King Philip Regional High School in Wrentham, MA, we in the chemistry department have created a goal to weave green chemistry throughout our curriculum, so we ask students to analyze every lab, identifying where it meets green chemistry principles and where it could be improved. While copper sulfate pentahydrate is not one of the worst culprits when it comes to disposal, we wondered how we could engage students in the greening of this lab. As such, we have substituted the use of Epsom salts or magnesium sulfate heptahydrate and use a hot plate instead of a Bunsen burner.
We were worried that the elimination of the color change seen with the dehydration of the copper compound would lessen the impact of the lab, but we were pleasantly surprised that, while a color change didn’t occur, definite physical changes were evident. Students were able to note a change in texture as well as a “popcorn effect” due to the removal of the water. Using the hot plate allowed for better control of the slow dehydration, also enabling students to obtain better results than they did with traditional the lab.
After using this "greener" replacement lab for the past two years, we have found that the vast majority of our students have been able to come up with the correct calculation of the formula. The added bonus to this replacement lab is that it generates rich discussions on the application of green chemistry principles. Students easily explain why the Epsom salt is less hazardous in terms of potential toxicity. At the same time, substitution of the hot plate has led to deep discussions on the safety of the hot plate over the burner vs. the need to heat the substance for a longer period at a low temperature. Our students were able to relate these discussions to several of the principles of green chemistry, including:
- Principle 3, as the Epsom salt is less hazardous to humans and the environment
- Principle 4, as Epsom salt serves the same function as the copper sulfate while reducing risk
- Principle 7, as the Epsom salt can technically be reused once it is rehydrated
- Principle 12, as the use of a less hazardous substance reduces the risk of accident
Find more information about greener replacement labs by visiting the Beyond Benign website
The American Chemical Society provides details about the 12 principles of green chemistry. You can download a pocket sized list of the principles on the same webpage.
Compound Interest created a handy version of the green chemistry principles.
Another take on a modified hydrate lab that could be tweaked by replacing copper II sulfate pentahydrate with magnesium sulfate heptahydrate : Cookbook to Inquiry -- Another Attempt