Download AlkaSeltzerLabConservationofMass

Alka-Seltzer Lab
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Big Question: Does mass change before and after a chemical reaction?
Materials: Triple beam balance, ziploc baggie, Alka-Seltzer tablet, water, graduated cylinder,
plastic cup
Hypothesis: Predict what will happen to the mass of the Ziploc bag before and after the Alkaseltzer reacts.
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Part 1 Procedures:
1. Obtain 100mL of water from the sink.
2. Obtain an Alka-Seltzer tablet from the teacher.
3. Place the Alka-Seltzer tablet in the small container provided.
4. Put the small container with the Alka-Seltzer tablet in the ziplock baggie standing it up so
the water does not mix with the Alka-Seltzer tablet inside.
5. Get as much of the air out of the ziploc baggie as possible and then seal the ziploc baggie
on top of the triple-beam-balance tray.
6. Measure the mass of the ziploc baggie and record it.
7. Making sure the ziploc baggie is sealed tight, remove it from the triple-beam-balance and
allow the container with the ziploc baggie to tip over and mix with the water.
8. After the chemical reaction in the baggie is complete, measure the mass of the ziploc
baggie again. DO NOT OPEN THE BAGGIE AT ALL DURING THE EXPERIMENT.
9. Compare the mass of the ziploc baggie before and after the reaction.
Part 1 Data:
Mass of the Water, AlkaSeltzer, baggy, and container
before the reaction. (grams)
Mass of the water, AlkaSeltzer, baggy and container
after the reaction. (grams)
Difference between the mass
before the reaction and after
the reaction. (grams)
Part 2 Procedures:
1. Carefully open the baggy and push all the air out.
2. Re-seal the baggy.
3. Place the baggy back on the triple beam balance. Without spilling, measure the new mass
and record.
4. Compare the mass of the ziploc baggie before opening and after opening.
Part 2 Data:
Mass of the water, Alka-Seltzer,
baggy and container before
opening the bag. (grams)
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Mass of the water, AlkaSeltzer, baggy and container
after opening the bag. (grams)
Difference between the
mass of the closed baggy
and the open baggy. (grams)
Questions:
1. Was the Alka-seltzer + water a chemical or physical change? How do you know?
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2. In part 1, was there a difference in the mass before and after the chemical reaction? Why
or why not?
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3. In part 2, was there a difference in the mass before and after you opened the bag? Why or
why not?
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4. Did you make any errors in this experiment? If so, explain.
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5. What is the law of conservation of mass?
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Answer Key:
1. Chemical change- gas was produced
2. In part one the mass stayed the same, mass was conserved.
3. In part two the mass should have decreased because we let the gas out of the bag.
4. Answers will vary by student.
5. Matter cannot be created or destroyed during a chemical reaction.
Teacher Notes:
If you have access to electronic scales you will get much more accurate results, but triple beam
balances work as well. I also use the Ziploc bags that have the slider top. They are much easier to
seal and you don’t have to worry about students spilling water all over.
If students measured correctly there should be NO change in the mass when the bag is sealed. I
do this lab before I teach the law of conservation of mass- let the students figure out the law
before you teach it to them.
In part 2, the mass will decrease since gas left the bag. This shows students that gas is produced
and that gas also has mass.
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