Name:
Reactions & Conservation of Mass Lab
Objectives: Observe the signs of a chemical reaction. Infer that a reaction has occurred. Compare
masses of reactants and products. Relate observations to the law of conservation of mass.
Background: The law of conservation of mass states that matter is neither created nor destroyed during a chemical
reaction. Therefore, the mass of a system should remain constant during any chemical process. In this experiment,
you will determine whether mass is conserved by examining a sample chemical reaction and comparing the mass of the
system before the reaction with its mass after the reaction.
Safety: Wear goggles and apron. Sodium bicarbonate is a skin irritant – do not touch.
Procedure: Part 1
1. Place a dime size amount of sodium bicarbonate into a small beaker.
2. Use a graduated cylinder to measure 30.0mL of 5% acetic acid solution, and pour it into a second beaker.
3. Place the two beakers side by side on the balance pan and measure the total mass of the system (before reaction).
Record the mass if the Data Table.
4. Add the acetic acid to the sodium bicarbonate a little at a time to prevent the reaction from overflowing out of the
beaker. Allow the acetic acid to slowly run down the inside of the beaker. Observe and record your observations about
the reaction.
5. When the reaction is complete, place both beakers on the balance and determine the total final mass of the system.
Calculate any change in mass. Record both the final mass and any change in mass in your Data Table.
6. Try to develop a modified procedure that will test the law of conservation of mass more accurately than the
procedure in Part 1. You will be allowed to use the same two chemicals, as well as a Ziploc bag and a twist tie or
rubber band.
Part 2:
7. Implement your procedure with the same chemicals and quantities you used in Part 1.
Record your data in Data Table.
8. Clean your lab station. Clean all equipment and return it to its proper place. Dispose of chemicals and solutions
down the drain with copious amount of water. Wash your hands. Discreetly write your name and your favorite
television show on a piece of paper and place it in my basket on the front counter before class begins.
Data:
Data Table: Initial and Final Mass
Part 1
1. Initial: Total mass of system (1+2) before reaction
2. Final: Total mass of system after reaction
3. Change in mass (1-2)
Part 2
Mass (g)
Calculations: On you notebook
paper - calculate the percent error
for your results from Part 1 as well
as for your results from Part 2.
Use this formula to calculate the
percent error:
Initial Mass – Final Mass X 100 =
Initial Mass
4. Initial :Total mass of system you created before reaction
5. Final: Total mass of system you created after reaction
6. Change in mass (4-5)
Conclusion Questions: Also answer on notebook paper
1. What evidence was there that a chemical reaction occurred?
2. In Part 1 how did the final mass compare with the initial mass of the system?
3. Does your answer to question 2 show that the law of conservation of mass was violated? (Hint: Another way to
express the law of conservation of mass is to say that the mass of all of the products equals the mass of all of the
reactants.)
4. Did the procedures for Part 1 or Part 2 give you a better percent error? Explain why you think this happened.
5. When a log burns, the resulting ash obviously has less mass than the unburned log did. Explain whether this loss of
mass violates the law of conservation of mass.
6. Design a procedure that would test the law of conservation of mass for the burning log described in question 5.