Density Determination

Marcea Anderson                 Thornton Township High School
                                150th & Broadway Ave.
                                Harvey, Il.  60426
                                708-596-1000

Objectives:

 (for jr. or sr. high school)
Purpose is to learn and practice techniques and calculations for determining 
volume and density of a substance.

Apparatus Needed:

Double pan balance, can of coke, can of diet coke, two evaporating dishes, 
sugar. (demo.)

Density vial. (demo.)

Recommended strategy:

     Start by having a density vial sitting on the front desk for the students 
to look at when entering the classroom. There are several kinds of denisty vials 
that you can make for the classroom.  A density vial uses several different 
solutions and objects in one container, each having a different density they 
will sink to their own level.  Start with a plastic liter bottle or jar or a 
large graduated cylinder.  Pour in small amounts of the liquid solutions first 
in the following order:  syrup (1.36 g/cc), glycerine (1.26 g/cc), ethylene 
glycol (1.11 g/cc), colored water (1.0 g/cc), oil (.9 g/cc),colored alcohol (.79 
g/cc).  Now, slide in the solid objects, they will sink to their level of 
density within the solutions:  lead piece (11.3 g/cc), rubber stopper (1.2 
g/cc), plastic piece (.9 g/cc), oak (.9 g/cc), cork .2 (g/cc).  
     Give the students time to look carefully at the vial to notice the 
different levels of the solutions and the objects placed in the vial.  Ask the 
students questions about the vial.  "What do you see in the vial?  Why is the 
cork floating near the top and the copper piece is near the bottom?"  Continue 
asking questions until the students come to some conclusion that the solutions 
and objects have different densities.  You may change this lesson some what by 
making the density vial as a demonstration.  At this point, set the density vial 
off to the side and tell the students that we will come back to this later in 
the class period. 
     Bring out your double pan balance and soda cans.  Ask the students about 
the mass and volume of the two sodas.  Then place the two cans on the balance, 
the regular coke should be heavier.  Ask the students why the regular coke is 
heavier.  Ask them what is in the coke that is not in the diet coke.  (Hint:  
nutrisweet is 200 times sweeter than sugar, so they only use a small amount of 
it in diet coke.)  Coke has a very sweet taste to it because of all of the sugar 
added to it. Then ask the students ways to determine how much sugar is in coke 
that is not in diet coke.  Hopefully, the students will tell you to put sugar on 
top of the diet coke can.  You can do this by placing an evaporating dish on top 
of each can, then add sugar to the dish on the diet coke can until the two cans 
are balanced, this will give you equal mass of the two cans.  Ask the students 
questions about the soda cans.  "What happened to the mass of each can?  What 

happened to the volume of the two cans?  What do you suppose that this can of 
each variable is telling us?" 
     At this point in the lesson, it will be necessary to explain the concept of 
density.  Talk about the variables in density and the formula for solving for 
density.  Go back to the denisty vial.  Once again ask the students questions 
about the vial, this time relating them towards the denisty of the various 
solutions and objects.  Your "recipe" for the density vial should list the 
various densities of the solutions and objects to be used.