Conservation of Mass Lab
Question: Do substances lose or gain mass during chemical reactions?
Materials:
electronic balance
100 ml graduated cylinder
glass jar with lid
Alka-Seltzer tablet
Procedure 1: With lid
1. Using the graduated cylinder, measure 50 ml of water and pour into the jar & put the
top on the jar.
2. DO NOT PUT THE TABLET IN THE WATER - Using the electronic balance,
measure the total mass of half an Alka-Seltzer tablet and the glass bottle containing 50
ml of water with the lid on. Put the tablet on top of the lid. Write the mass in the data
table.
3. On the table, open the bottle and put tablet in the water. Quickly put the lid on and
tighten.
4. Allow the tablet to dissolve completely.
What do you observe?
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5. Do not remove the lid. Measure the mass of the bottle, water, and dissolved tablet
and record in the table.
Procedure 2: Without lid
1. Clean your jar out thoroughly & dry it off.
2. Using the graduated cylinder, measure 50 ml of water and pour into the jar
3. DO NOT PUT THE TABLET IN THE WATER - Using the electronic balance,
measure the total mass of half an Alka-Seltzer tablet and the glass bottle containing 50
ml of water without the lid. Record in the second table.
4. Drop the tablet in the water and allow to dissolve completely.
5. Measure the mass of the bottle and water. Record in the second table.
Data:
Procedure 1: With Cap on Bottle
Mass of jar, lid, & ½ of the tablet
Mass of jar, lid, & ½ of the tablet
Difference between the
Before
After dissolving
masses (before – after)
Mass of jar & ½ of the tablet
Mass of jar & ½ of the tablet
Difference between the
Before
After dissolving
masses (before – after)
Procedure 2: Without Cap on Bottle
Questions:
1. Did a physical change occur at any time during this experiment?______
What evidence do you have of that?
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2. Did a chemical change occur at any time during this experiment? _____
What evidence do you have of that?
______________________________________________________________________
______________________________________________________________________
3. Explain why the mass of the closed bottle was the same before and after the reaction
took place.
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4. Explain why the mass of the open bottle was less after the reaction took place.
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5. During a chemical reaction, does the total amount of mass change? ________
What law can be used to explain you answer? ___________________________
6. The chemical formula for this reaction is:
____NaHCO3 + ____H3C6H5O7 -----> ___CO2 + ___H2O + ___Na3C6H5O7
List the different elements and the number of atoms of each.
Reactants
Products
Challenge: Balance the equation