Name ___________________________________
Period _______ Points ________/15
Lab: Law of Conservation of Mass
Objective: The purpose of this law is to prove the law of conservation of mass using a very simple
reaction – vinegar & baking soda! Before you begin, answer the questions below.
1. The law of conservation of mass states that ___________________________________________________
______________________________________________________________________________________
2. Why is it hard to prove the law when a gas is produced? _________________________________________
______________________________________________________________________________________
3. What is the difference between an “open” system & a “closed” system? _____________________________
______________________________________________________________________________________
______________________________________________________________________________________
Materials: 2 beakers labeled A & B, balance, vinegar, baking soda, plastic bag, plastic spoon
Part 1: Open System
1. Calibrate the balance to 0.
2. Label two beakers A & B.
3. Fill beaker A with 20 mL of vinegar.
4. Add 1 spoonful of baking soda into beaker B.
5. Place both beakers on the balance & record the starting mass.
6. Dump the baking soda into beaker A. Do not stir.
7. Place both beakers on the balance & record the ending mass.
8. Calculate the amount of mass changed by subtraction.
Baking Soda & Vinegar:
Open System
Starting mass: ___________ g
Ending mass: ____________ g
Amount Changed: ________ g
Part 2: Closed System
9. Clean & dry both beakers.
10. Fill a beaker A with 30 mL of vinegar.
11. Add 1 spoonful of baking soda into a clean plastic bag.
12. Gently place beaker A in the plastic bag without spilling the vinegar.
13. Try to push all air out of the bag. Seal the bag & place it on the balance without spilling the vinegar.
Record the starting mass.
Baking Soda & Vinegar:
14. Without opening the bag, tip the beaker to mix the vinegar with the
baking soda.
15. Still without opening the bag, record the ending mass of the
contents of the plastic bag.
16. Calculate the amount of mass changed by subtraction.
Closed System
Starting mass: ___________ g
Ending mass: ____________ g
Amount Changed: ________ g
Cleanup: Return the balance to the back counter. Clean & dry the beakers and the plastic bag. Please
return bins to the windows with supplies organized according to the picture.
Think About It
Below is the chemical equation for this reaction.
1. What are the reactants? __________________________________________________________________
2. What are the products? __________________________________________________________________
3. Count the number of elements on each side of the equation & write the total number down below.
Reactants
Products
_______ Hydrogen
_______ Hydrogen
_______ Oxygen
_______ Oxygen
_______ Carbon
_______ Carbon
_______ Sodium
_______ Sodium
4. Is this reaction “balanced”? Explain.
5. Compare the open system (part 1) to the closed system (part 2). What was the same? What was different?
6. Did this lab prove the law of conservation of mass? Explain & use data to support your answer.