I typically evaluate this activity through class participation although the answer key is posted after class to let the students evaluate their own understanding of concepts. The students do know that they will be tested on the material within the activity and usually I have a density problem on the exam.
This activity is designed to give the students more freedom as they move from the first density calculation to the last set of calculations. Within the last set of calculations, they encounter a hexagonal unit cell so that may require some additional intervention to get them to think about how to calculate the volume of a hexagonal unit cell.
This activity is designed to relate solid-state structures to the density of materials and then provide a real world example where density is used to design a new method to explore nanotoxicity in human health. Students can learn how to calculate the density of different materials (gold, cerium oxide, and zinc oxide) using basic principles of solid state chemistry and then compare it to the centrifugation method that was developed to evaluate nanoparticle dose rate and agglomeration in solution.
A student should be able to calculate a unit cell volume from structural information, determine the mass of one unit cell, and combine these two parameters to calculate the density for both cubic and hexagonal structures. In addition, students will have an opportunity to read a scientific article and summarize the major findings, place data in a table, and explain the similarities and differences between the densities calculated in the activity and the experimental values that are reported in the literature.
I have used this activity in our first semester inorganic chemistry course when we cover solid-state materials. One thing to note is that I do use 2-D projections to describe structures and we cover that in a previous activity. You could remove 2-D projections from this activity if it is not something that you previously covered.