The Conservation Of Mass (The Mass Of Gas)

Jake Carter                    Douglass Math and Science Academy
                               543 North Waller 
                               Chicago IL 60644
                               (312)543-6176

Objectives:

      This experiment will help students with their understanding of matter in 
all of its phases.  It will show that in a chemical reaction where a gas is 
produced, the mass does not change.  The mass does not change provided none of 
the gas is allowed to escape.  This will give evidence for conservation of 
mass.  In furthering their knowledge of the laws of conservation of mass, the 
loss in mass can be accounted for, when the gas is allowed to escape from the 
container which it is produced in.  This will prove that gas does have mass.  

Materials Needed:
                     
  Balance                           1/8 Alka-Seltzer tablet
  Pegboard and clamps (optional)        Paper towel
  Small, thick-walled bottle with       Safety glasses
     tight-fitting cap                  Tape

Strategy:

     Students are asked to work with their lab partner to carry out this 
experiment.  The Students will collect all materials from the teacher's   
material lab station in the front of the room.  The students must return to 
their lab stations to set up the apparatus.  Now, begin by massing the small 
thick-walled bottle, 3/4 full of water, the cap and the 1/8 piece of Alka-
Seltzer tablet on the balance.  The initial massing of the bottle, cap, water, 
and 1/8 piece of Alka-Seltzer tablet should be recorded on the sample data 
graph. 
     The final massing of the small, thick-walled bottle, cap (put the Alka-
Seltzer table in the water) and solution should now be done.  Record your 
results on the data graph.  To avoid any gas from escaping the students must 
work quickly to drop the 1/8 Alka-Seltzer tablets into the bottle of water and 
close the cap.  Students should at this time compare data from the initial 
massing with that of the final massing.  The students are now ready to 
complete the final part of the experiment.  The cap on the bottle should be 
loosened slowly, so that no water bubbles out when the gas escapes.  When the 
gas escapes, the solution shows a small change in mass.  Record the data on the
data graph.  The mass difference would suggest that:__________________________. 
Repeat the entire experiment for a second time, record and compare results. 

Performance Assessment:

1.  The student will be able to communicate their results of the experiment
    in a written lab report, using a standard lab reporting form.
2.  They will be able to articulate the experiment in our post lab 
    discussions.
3.  Students will create a scientific graph showing results of the experiment.
4.  Students will be able to draw conclusions about the conservation of matter
    based upon the experiment.