Chemistry Lab: Composition of a Hydrate

This is one of my favorite chemistry labs and here's why: It has a simple materials list. It is easy to set up and break down. It yields great results. It provides a quality lab during your unit on chemical formulas, a unit in which labs are hard to come by. It has a mathematical component which students need. Students calculate percent error. Students learn how to write the formula of a hydrate. Students compare experimental data to theoretical data, which is so important!

That's a lot of reasons why you should do this lab! 

Here is the link in my TPT store:  Composition of Hydrates Lab

It's best to use this lab when teaching your unit on how to write chemical formulas and how to name chemical compounds. Hydrates are compounds that have some number of water molecules attached to them. The premise of the lab is simple: A known mass of a hydrate is heated to release the water of hydration. The mass of the resulting anhydrous salt is determined. The difference in the mass of the hydrate and the mass of the anhydrous salt can be used to determine the formula of the compound.

In our lab, we used copper (II) sulfate pentahydrate. A fine crystal is needed for the lab. Since we only had the medium crystal in stock, my students used a mortar and pestle to grind the crystals into a finer powder.

The hydrate is heated over a Bunsen burner in an evaporating dish to remove the water of hydration. But first the empty evaporating dish must be heated to remove all water, allowed to cool briefly, and the mass of the empty dish determined. 

The difference in the "before mass" and the "after mass" is used to determine the mass of water lost. Students are given directions in how to use this information to determine that the compound used was copper (II) sulfate pentahydrate. 

I love the simplicity of this lab and the fact that my students clearly understood how to use this data to determine the formula of the compound. All in all, it's a great day in the lab!