Name:___________________________________________________________________________________
LAB: CONSERVATION OF MASS
Problem of Study: The problem is determining if there is a mass change during a chemical reaction.
Independent Variable
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Dependent Variable
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Background:
What do you already know about chemical reactions that might help you answer this questions?
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NULL HYPOTHESIS:
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Materials: Balance
Alka-seltzer tablets
Beaker
Graduated cylinder
empty bottle with cap
Procedure and Results:
1. Measure 200ml of water and carefully pour it into the empty plastic bottle. Recap the bottle
2. Mass an Alka-Seltzer tablet and the plastic bottle containing 200ml of water with the cap on.
Mass of the “system” BEFORE combining. System is ( bottle with cap, alka-seltzer and water )
3. With the bottle on the lab bench, place a tablet in the bottle and IMMEDIATELY screw the cap on
VERY Tightly.
4. Place the closed bottle back on the balance and mass it AGAIN.
Mass of the “system” with closed cover
5. Wait until the Alka-seltzer tablet has completely dissolved. Place the bottle on the lab bench and
SLOWLY loosen the cap and leave the bottle uncapped.Wait 30 seconds. Place the cap and filled
bottle back on the balance and find the mass of the “system”
Mass of the “system” (bottle, cap, alka-seltzer and water) with the cap off – OPEN system
6. Repeat step 1 -5 four more time
DATA:
Replicate
System Mass Before
Combination
System Mass After
Combination- CLOSED
System Mass After
Combination-OPEN
1
2
3
4
5
Analysis: Run a statistical t test to compare your two sets of results
p-value:_________________________________________________________________________________
Conclusion:
Do you accept or reject your null hypothesis? Why?
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Questions: Answer on back
1. Did a physical change occur at any time during this experiment? What evidence do you have of
that?
2. Did a chemical change occur at any time? What evidence do you have of that?
3. Was the mass of the closed bottle system AFTER the chemical reaction (step 4) the same as the
mass of the uncombined system, BEFORE the reaction (step 2)?
If not, attempt to explain why not.
4. Determine the mass of gas released in this process for all five replicates and find the average.
5. Looking at the package or other resources, write the chemical reaction and balance the chemical
reaction.
6. What gas was released in this reaction?
7. Using the average amount of gas released, how many moles of gas was released?