Law of Conservation of Mass Lab
Work Guide
8th Grade Essential Standards
8.P.1.4: Explain how the idea of atoms and a balanced chemical equation support the conservation of mass
PURPOSE
To observe and verify the Law of Conservation of Mass - In any chemical reaction, the total mass of the
reactants is always equal to the mass of the products.
INTRODUCTION
The word equation for the following reaction is as follows:
vinegar + baking soda → sodium acetate + water + carbon dioxide
The chemical equation for the reaction is:
CH3COOH + NaHCO3 → NaC2H3O2 + H2O + CO2
SCIENTIFIC QUESTION
When vinegar and baking soda are combined, how can the law of conservation of mass be observed from this
chemical reaction?
HYPOTHESES
MATERIALS
 balance
 beaker
 1 balloon
 paper
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empty water bottle
graduated cylinder
5 g baking soda
15 mL vinegar
PROCEDURE
* Wear safety goggles and a lab apron for this activity.
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Using a balance, record the mass of the empty water bottle.
Using a graduated cylinder, measure 15 mL of vinegar
Pour about 15 mL of vinegar into the empty water bottle.
Obtain the mass of the water bottle & vinegar. Record the mass of vinegar only.
Put a paper on top of the balance and weigh 5 g of baking soda. Record the mass of baking soda.
Record the weight of the balloon.
Carefully transfer the baking soda into the balloon.
While one student holds the empty water bottle with vinegar, another must slip the open end of the
balloon over the mouth of the empty water bottle, while keeping the baking soda from entering the
water bottle with vinegar.
9. When ready, tip the balloon upright, allowing the baking soda to drop into the empty water bottle
and allow the reaction to fully complete. (See Figure 1)
10. Measure and record the mass of the products/container/balloon. (See Figure 1)
11. Clean up all lab equipment, wash glassware and dispose of chemicals according to your teacher’s
instructions.
12. Return safety googles and aprons.
Figure 1
DATA AND RESULTS:
Calculate initial mass of reactants vs. final mass of products.
Mass of Vinegar Mass of Baking
in grams
Soda in grams
Total Mass of REACTANTS
in grams
-Vinegar and Baking Soda
only
(Before the reaction)
Total Mass of PRODUCTS in grams Vinegar and Baking Soda only
(After the reaction)
ANALYSIS QUESTIONS
1. What evidence was there that a chemical reaction occurred?
2. How did the final mass of the product compare with the initial mass of the reactants? Did it support the law
of conservation of mass? Justify your answer.
3. How else could you have tested the law of conservation of mass for this reaction?
CONCLUSIONS
Based from the data you collected is your hypothesis right or wrong? Explain your answer.
RECOMMENDATIONS
Discuss possible errors that could have occurred in the collection of the data (experimental errors)
REAL WORLD APPLICATION
List one thing you learned and describe how it applies to a real-life situation.