One investigatory project example that's a complex but very impressive project is spectroanalysis. "Spectroanalysis" is a fancy word for analyzing the spectrum of an object, usually given off when the object is burned. To perform this experiment, you'll need a Bunsen burner or other heat source, some things to burn, and a diffraction grating. You can obtain these supplies from Edmonds Scientific (see the link below). As for the objects to burn, wood, salt, sugar, and various nitrate salts work magnificently. Just make sure you have a few samples of each item. Burn each chemical on a small wood stick individually and observe the color of the flame with and without the diffraction grating, which separates the flame into its component colors or spectrum. Observe that each chemical gives off a different spectrum. This spectrum can be used to identify the chemical very accurately. Each chemical emits a different spectrum when burnt. By recording this spectrum, you can identify a chemical based on how similar its spectrum is to known spectra given off by other chemicals.