[Date]
Chemistry Lab: Conservation of Mass
Introduction
The French scientist Antoine Lavoisier (1743-1794) found that in a chemical reaction the mass of the
products is always the same as the mass of the reactants that react to form them. The law of
conservation of mass summarizes these findings. Matter is neither created nor destroyed in a chemical
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findings and try to confirm the law of conservation of mass. You will also use this law to calculate the
amount of oxygen used in a chemical reaction.
Purpose
Confirm the law of conservation of mass
Pre-Lab Questions
1. State the Law of Conservation of Mass.
[ your answer…]
2. According to the law of conservation of mass, if 16g of oxygen and 2 g of hydrogen react completely
to form water (nothing else), how many grams of water will be formed?
[______g]
Observations
Part A Barium chloride and Acid
Mass of flask before reaction
……….
.g
Mass of flask after reaction
……….
.g
Calculated difference
……….
.g
(Do not round, include unit
(grams), and calculate the
difference of the total masses
of before and after the
reaction)
Observations: [Your Observations … (write down all you see)]
Explain your experimental errors that led to a difference in the total masses before and after (if there is)
Er
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…]
Part B Acid and Base
Mass of beaker with tubes before reaction……….
.g
Mass of beaker with tubes after reaction……….
.g
Calculated difference
……….
.g
Observations: [Your Observations … (write down all you see)]
1
(Do not round, include unit
(grams), and calculate the
difference of the total masses
of before and after the
reaction)
Explain your experimental errors that led to a difference in the total masses before and after (if there is)
Er
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…]
Part C Calcium chloride and Baking soda
Mass of flask+ balloon before reaction
……….
.g
Mass of flask + balloon after reaction
……….
.g
Calculated difference
……….
.g
(Do not round, include unit
(grams), and calculate the
difference of the total masses
of before and after the
reaction)
Observations: [Your Observations … (write down all you see)]
Explain your experimental errors that led to a difference in the total masses before and after (if there is)
Er
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…]
Part D Burning Magnesium
Mass of crucible
……….
.g
Mass of magnesium
……….
.g
Total mass before reaction (add above #s)
……….
.g
Mass of crucible and residue afterwards
……….
.g
Calculated difference (= mass of oxygen)
……….
.g
(Do not round, include unit
(grams)
Observations: [Your Observations … (write down all you see)]
Conclusion
1. Parts A, B, C: Discuss whether your experimental results from Parts A-C verify the Law of
Conservation of Mass! If not, what went wrong? suggest improvements. (if your data showed no
error at all you were cheating!!!!) Write one paragraph in complete sentences [
….
.
]
2. What is important when conducting experiments to make your data meaningful and reliable?
[
….
.
]
3. Part D: From your measurements of Part D add mass of magnesium and mass of oxygen. This
will be the amount of magnesium oxide you produced in your experiment. Use this to complete the
sentence:
According to the Law of Conservation of matter I needed ______________ g of oxygen and _____ g
of magnesium to produce ____________ g of magnesium oxide.
4. List at least six different observations from all your experiments you conducted today that
indicated a chemical reaction took place. [
…]
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Chemistry Lab: Conservation of Mass
Safety
Wear your goggles at all times during this lab. Be especially cautious about sulfuric acid and
barium compounds in this lab. Let heated items cool down a few minutes before proceeding.
Do not look directly into the crucible when the magnesium is burning. You could damage your
retina.
Procedure
Part A
Materials needed: balance, 125-ml Erlenmeyer flask, stopper
a small test tube that can fit inside the flask, forceps
1.
2.
3.
4.
5.
6.
Pour 25 ml of barium chloride solution into a clean 125-ml
Erlenmeyer flask.
Pipette 5 ml of dilute sulfuric acid into a small test-tube. Using
your forceps, place the test-tube into the flask.
Insert the stopper. Make sure you have a tight seal. Mass the flask. Record the mass.
Holding the stopper tight, carefully invert the flask a few times to mix the contents well (hold up
side down and back). Record any changes you observe in your lab journal.
Mass the flask again on the same balance. Record this mass.
Pour solution into the designated waste container and rinse glassware and stopper thoroughly.
Part B
Materials needed: balance, 250-ml beaker, 2 medium size test tubes
1.
2.
3.
4.
5.
6.
7.
Fill one test tube with 5 ml of dilute sulfuric acid.
Fill another test-tube with 5 ml of ammonia water.
Place the 2 test tubes upright in the beaker, which acts as a holder.
Find the mass of the assembly and record the result.
Remove the beaker with test tubes from the balance and place it on
your lab bench. Carefully pour the contents of one tube into the
other test tube without spilling!
Observe any evidence of a chemical change when the chemicals are mixed.
Re-determine the mass of the assembly using the same balance. (Your beaker should still contain
two (2) test tubes, one empty and one filled.) Record the mass.
Rinse all glassware at your sink thoroughly. (no special waste disposal necessary).
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Part C
Materials needed: balance, balloon, 125-ml Erlenmeyer flask.
1.
2.
1.
2.
3.
5.
6.
7.
8.
9.
Take a balloon and carefully stretch it. Add two (2) scoops
of calcium chloride and (1) scoop of
sodium
hydrogen
carbonate to the stretched balloon. Shake gently to mix.
Determine the mass of the balloon and its contents.
Measure 25 ml of distilled water into a graduated cylinder.
Add this water to a 125-ml Erlenmeyer flask.
Add 5 drops of indicator. Determine the combined mass of the flask . Record the mass.
Slip the balloon over the neck of your Erlenmeyer flask without losing any solids out of the
balloon. Make sure you have a tight seal between the flask and the balloon.
Lift (and lightly shake) the balloon to allow the solids to fall into the flask. Swirl the flask gently
to allow the solids and liquid to mix.
Observe the reaction until it comes to a stop. Record all your observations. (temperature change)
Record the mass of the flask and its contents.
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Return all equipment to the areas from where you picked it up. Clean and dry your lab bench.
Part D will be done after everybody finished with Parts A-C
Part D Using the Law of Conservation of Mass
Materials needed: balance, ring stand, ring clamp, clay triangle,
crucible with cover, Bunsen burner one piece of magnesium .
Oxidation of magnesium
1. Determine the mass of a crucible and a piece of magnesium
ribbon separately. Fold the magnesium ribbon so that it fits
into a crucible. Put the magnesium into the crucible,
2.Place the crucible on a clay triangle on a ring clamp and ring
stand as shown in Figure A. Partially cover the crucible; the
cover should be skewed slightly to the side so that the
magnesium can be seen.
3. Begin to heat the crucible with a low flame. When the
magnesium glows for three seconds, stop the heating.
4. Wait 5 minutes to let it cool down!!!!
5. Record all your observations before returning the crucible to the balance to determine the mass after
the completed reaction.
6. Discard the cold solid in the garbage and rinse the crucible.
Clean your lab bench, wash your hands and return your safety goggles into the cabinet.
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