2 comments By Michael
I really like this experiment - it's good for an open investigation.
As an extension, you can get pupils to work out whether the shape of the sample makes a difference (eg. what's the area of the 10cm square, can we cut out a triangle with that area, etc).
I taught Chemistry and Physics for thirty years. I developed a teaching tool based on the long form of the period table. Students gained a true insight into the arrangement of the periodic table from this long form. Actually cut up a standard periodic table wall chart and put it back together in the long form in the 80's. Also rounded all atomic masses to three significant digits. Having four, five, or even six digits at the middle/high school level is cumbersome and is not needed.