Section 16: Chemical Equations
[CONSERVATION OF MASS LAB]
Purpose
The purpose of this lab is to compare and contrast the law of conservation of mass in a close versus an open system.
Introduction
The law of conservation of mass, also known as the principle of mass/matter conservation, states that the
mass in a closed system will remain constant over time. This principle is equivalent to the conservation of energy, in
the sense when energy or mass is enclosed in a system and none is allowed in or out, its quantity cannot otherwise
change (hence, its quantity is "conserved"). The mass of an isolated system cannot be changed as a result of
processes acting inside the system. The law implies that mass cannot be created or destroyed, although it may be
rearranged in space and changed into different types of particles; and that for any chemical process in a closed
system, the mass of the reactants must equal the mass of the products.
Laboratory Procedure
You will be doing this experiment twice: once in an open system, once in a closed system.
 Find the mass of your container.
 Add about 10 g of baking soda to your container.
 Measure out 20 mL of vinegar and determine it’s mass.
 Add the vinegar to the open system and allow it to finish reacting. Determine the total mass after.
 Carefully add the vinegar to the closed system and immediately zip the bag shut. Determine the total mass
after the reaction is complete.
Open system:
Closed system:
Mass
Beaker
Vinegar
Baking Soda
Total Before
Total After
Mass
Zip-Lock Baggie
Vinegar
Baking Soda
Total Before
Total After
Post-Lab Questions
1. What evidence was there that a chemical reaction occurred?
2. Was the law of conservation of mass violated or proven?
3. What were the differences between the open system and the closed system?
4. When a log burns, the resulting ash obviously has less mass than the unburned log did. Does this violate the
law of conservation of mass?
5. Design a procedure that would test the law of conservation of mass for the burning log.