This Laboratory has students get out of their seats to see how important the concept of molar mass (molecular mass) is. Students weight out a given sample provided by the teacher (I usually used salts and some metals). From that mass and the provided number of moles, students calculate the molar mass and identify what substance they are looking at.
Great for an activity to get students out of the seats. I prepare the "chemicals" once in test tubes with stoppers and use them year after year.
Can be used as a teaching tool, or guided practice.