7
Conservation of Mass in a Chemical Reaction
In a chemical reaction, mass is never created or destroyed. This means that if we can keep track of the mass of
all reactants used and all products formed, we should find the final mass unchanged.
In this reaction, we will combine solution of sodium carbonate, Na2CO3 and calcium chloride, CaCl2. These
chemicals will undergo a double replacement reaction. With careful technique, you will find that the total
mass of the products equals the total mass of the reactants.
Compound “A” + Compound “B”  Compound “C” + Compound “D”
CaCl2
+
Na2CO3

Objectives:
To verify with measurements that mass is conserved during a chemical reaction
To explain how errors made during the lab contribute to a “gain” or a loss of mass.
Materials:
Two 250 mL beakers
Filter Funnel
Filter Paper
Pencil
Ring Stand
Ring Clamp
Calcium Chloride
Bunsen Burner
Drying Oven
Sodium Carbonate
DI Water
Procedure:
1. Use a pencil to label two clean, dry 250 mL beakers –one with “A” and one with “B”. Record each mass
of each beaker to the nearest 0.1 g.
2. Obtain approximately 0.5 g of CaCl2 (Compound “A”) and place it in Beaker A. Record the total mass.
3. Obtain approximately 0.5 g of Na2CO3 (Compound “B”) and place it in Beaker B. Record the total mass.
4. Obtain 12-18mL of DI water in a graduated cylinder. Add the water to Beaker A. Obtain another 12-18
mL of DI water graduated cylinder and add it to Beaker B. Swirl the contents of the beakers until all of
the solids have dissolved and the solutions are clear. DO NOT use a stirring rod, as this will cause a loss
of compound
5. Slowly add the Na2CO3 from Beaker B into the CaCl2 solution in Beaker A. A white precipitate should
form.
6. Wash the sides of Beaker B with a SMALL amount of DI water from the squirt bottle. Pour this water
into Beaker A. (This step assures that virtually all of the Na2CO3 has been transferred to the second
beaker.)
7. Gently heat the mixture in Beaker A until it reaches the boiling point. This will convert all reactants to
products.
8. Allow the beaker and contents to cool while setting up the filtering apparatus (ring stand, ring, and
funnel)
9. Obtain a piece of filtering paper. Get the mass of the filter paper then fold the paper as shown by the
teacher and place it in the funnel.
10. Place the empty Beaker B below the funnel to catch the solution as it passes through the filter
11. Pour the contents of Beaker A through the filter paper, being careful to keep as much of the precipitate
in Beaker A as possible. Rinse the precipitate several times with SMALL amounts of DI water. Do not
use a stirring rod to decant.
12. When filtering is complete, remove the filter paper from the funnel and place it in Beaker A with the
precipitate. Allow filter paper and precipitate to dry in oven overnight. Measure the final mass of dry
compound “C”, filter paper, and Beaker A.
13. Place Beaker B containing the filtrate paper on top of a wire mesh and ring stand. Gently heat this
solution to evaporate most of the liquid. CAUTION: DO NOT heat to dryness, as this will cause a loss of
product or a cracked beaker.
14. Let Beaker B and compound “D” dry overnight. Measure the final mass of Beaker B and compound “D”.
15. After all final mass measurements have been obtained, discard the filter paper and clean all beakers.
7
Conservation of Mass in a Chemical Reaction (M)
In a chemical reaction, mass is never created or destroyed. This means that if we can keep track of the mass of
all reactants used and all products formed, we should find the final mass unchanged.
In this reaction, we will combine solution of sodium carbonate, Na2CO3 and calcium chloride, CaCl2. These
chemicals will undergo a double replacement reaction. With careful technique, you will find that the total
mass of the products equals the total mass of the reactants.
Compound “A” + Compound “B”  Compound “C” + Compound “D”
CaCl2
+
Na2CO3
 __________ + __________
Objectives:
To verify with measurements that mass is conserved during a chemical reaction
To explain how errors made during the lab contribute to a “gain” or a loss of mass.
Materials:
Two 250 mL beakers
Filter Funnel
Filter Paper
Pencil
Ring Stand
Ring Clamp
Calcium Chloride
Bunsen Burner
Drying Oven
Sodium Carbonate
DI Water
Procedure:
1. Use a pencil to label two clean, dry 250 mL beakers
–one with “A” and one with “B”. Record each
mass of each beaker to the nearest 0.1 g.
2. Place 0.5 g of CaCl2 (Compound “A”) in Beaker A. Record the total mass. ____________ g
3. Place 0.5 g of Na2CO3 (Compound “B”) in Beaker B. Record the total mass. ____________ g
4. Fill a small graduated cylinder
to the top with distilled water. Add the water to Beaker A. Fill the
graduated cylinder again with distilled water and add it to Beaker B. Swirl the contents of the beakers
until all of the solids have dissolved and the solutions are clear. DO NOT use a stirring rod, as this will
cause you to lose some of the compound.
5. Slowly pour the contents of Beaker B into the solution in Beaker A. You should notice a white
precipitate should form. *Remember, a precipitate is a solid formed in a liquid during a reaction.
6. Wash the sides of Beaker B with a SMALL amount of DI water from a squirt bottle. Pour this water into
Beaker A. (This step assures that virtually all of the Na2CO3 has been transferred to the second beaker.)
7. Gently heat the mixture in Beaker A until it reaches the boiling point. This will convert all reactants to
products.
8. Allow the beaker and contents to cool while setting up the filtering apparatus (ring stand, ring, and
funnel)
9. Obtain a piece of filtering paper. Get the mass of the filter paper then fold the paper as shown by the
teacher and place it in the funnel.
10. Place the empty Beaker B below the funnel to catch the solution as it passes through the filter.
11. SLOWLY pour the contents of Beaker A through the filter paper, being careful to keep as much of the
precipitate (the solid) in Beaker A as possible. Rinse the precipitate several times with SMALL amounts
of DI water. Do not use a stirring rod to decant.
12. When filtering is complete, remove the filter paper from the funnel and place it in Beaker A with the
precipitate. Allow filter paper and precipitate to dry in oven overnight. Measure the final mass of dry
compound “C”, filter paper, and Beaker A.
13. Place Beaker B containing the filtrate paper on top of a wire mesh and ring stand. Gently heat this
solution to evaporate most of the liquid. CAUTION: DO NOT heat to dryness, as this will cause a loss of
product or a cracked beaker.
14. Let Beaker B and compound “D” dry overnight. Measure the final mass of Beaker B and compound “D”.
15. After all final mass measurements have been obtained, discard the filter paper and clean all beakers.
Data Table: Reactants
Total mass of beaker A and CaCl2
Mass of beaker A
Subtract to get the mass of CaCl2
Total mass of beaker B and Na2CO3
Mass of beaker B
Subtract to get the mass of Na2CO3
Add the masses of CaCl2 and Na2CO3 (Reactants)
Data Table: Products
Mass of the filter paper, Beaker A, CaCO3
Mass of the filter paper
Mass of Beaker A
Subtract to get just the mass of CaCO3
Mass of the beaker B and NaCl
Mass of beaker B
Subtract to get the mass of NaCl
Add the masses of CaCO3 and NaCl (Products)
Analysis Table:
Subtract the mass of the Reactants from the products
(the last line from the reactant and product tables)