Many chemistry teachers use a hydrate lab in their classroom. Students have some type of hydrate, usually copper (II) sulfate pentahydrate because of its beautiful color change, and dehydrate it over a Bunsen burner. It’s a great lab activity because it can assess so many different things: Bunsen burner lighting and safety, percent composition, percent error, accuracy and precision and the concepts of lab procedures and safety.
Due to a lack of supplies and chemicals in my early years, I instead use food. And while I now have access to a lab, this activity is so simple, it’s worth continuing. Plus it’s fun, and that’s what I’m all about!
Background
A hydrate (the noun) is an ionic chemical in the solid form that holds on to water molecules. It’ll actually grab on to a specific number of those water molecules per unit of the crystal lattice. So, for example, copper II sulfate will hold onto 5 water molecules. This makes it copper II sulfate pentahydrate. But those water molecules are physically attached to the lattice. So a simple physical change, (like heating and drying the salt) will remove the water. There are some hydrates that are a different color when they are hydrated versus dry. So if I were to do this lab in the classic way, I’d want to use copper II sulfate pentahydrate so my students could see it change from blue to white as it dried.
I sort of demonstrate the image below using a Hobberman sphere and a tennis ball (or something similar) “trapped” inside.
Supplies & Set Up
The food in this hydrate lab is bubble gum. I use some really cheap bubblegum with a high sugar content. The only other supply needed is a food safe balance. If my school didn’t have one, I would have just borrowed my kitchen scale from home.
When there are no chemicals, or you simply don’t feel like dragging out the Bunsen burners and hot plates here’s the set up:
- Bubble gum = hydrated salt
- Wrapper = crucible
- Chewed bubble gum = dehydrated salt
- Sugar = water
Students take the mass of the bubble gum before and after they chew the gum to find out the mass of sugar removed from the gum.
Sources of Error
The skills the students do in my version of the lab are the same as the copper (II) sulfate pentahydrate version, with the exception of the Bunsen burner specific things. The only real difference is that my students always have a very high percent error. The reason for this is because as they are removing sugar, they are actually adding saliva. Therefore the mass isn’t dropping as much as it should. I make sure that this comes up in our post lab discussion so they can write up proper lab reports. Read about the way my students write lab reports here. Those lab reports require some pretty decent reports, which I have a rubric for. Grab your free copy of my lab rubric here.
Get Help
I have this lab activity available in my TPT store. It is also included in my year long chemistry lab manual. The lab manual contains 41 lab activities that are just like this one. Super low maintenance, nearly chemical free and simple to set up and take down.
