Conservation of Matter
Chemical Reactions
• Happen all of the time
• Happen naturally or can be man made
• Can be physical or chemical
Rules for Reactions
• Matter cannot be created or destroyed!
• The total amount of matter remains constant
Using what we just learned answer the
following question.
• Is magic real?
– Why or why not?
– VIDEO!
History of this Concept
• Antoine Lavoisier
– 1700’s
– Studied chemical reactions
– Concluded that the mass before
a reaction occurred was the
same as the mass after the
reaction occurred
– This helped shape what we know
today
Law of Conservation of Matter
• During a chemical reaction,
matter cannot be created or
destroyed.
• Even though the matter may
change from one form to
another, the same number of
atoms exists before and after
the change takes place!
More specifically…
• The mass of the reactants must equal the
mass of the products.
Reactant + Reactant =
Mass of
Reactants
Product
Mass of
Products
Example: Tin Fluoride
• Tin + hydrogen fluoride -> tin fluoride + hydrogen
40.02 g
118.7 g
• What’s the total mass of the reactants?
– 158.72 g
• So what should the mass of the products be?
– 158.72 g
• Tin + hydrogen fluoride -> tin fluoride + hydrogen
Total Mass of
Reactants: 158.72 g
• If we know the mass of the tin fluoride, can
we figure out how much hydrogen was
produced?
– Subtract the mass of one product from the total
mass.
Lab Summary
• Plastic Bag
Initial Mass
Final Mass
22.9 g
22.7g
Change in
Mass
-0.2 g
• Beaker
Initial Mass
Final Mass
21.4 g
20.9g
Change in
Mass
-0.5 g
Plastic Bag Procedure
1. Place 2 g of baking soda into a small plastic
cup.
2. Place 10 mL of vinegar into a small plastic cup.
3. Put both cups in the plastic bag. Take care
NOT to spill the contents of either cup.
4. Seal the plastic bag.
5. Determine the mass of the cups and their
contents, and the plastic bag. Write the values
in your data table.
6. Without opening the bag, pour the vinegar
into the cup of baking soda.
7. Observe
8. Without opening the bag, record the mass of
the contents of the plastic bag. Take care not
to break the seal of the plastic bag.
Initial
Mass
22.9 g
Final Mass
22.7g
Change in
Mass
-0.2 g
Beaker Procedure
1. Place 2 beakers on the balance
2. Press zero
3. Measure 2 g of baking soda in the smaller
beaker (50 mL)  50 mL is the size of the beaker
4. Pour 20 mL of vinegar into the larger beaker
(100 mL)  100 mL is the size of the beaker
5. Write your mass in your data table.
6. Without spilling, pour the baking soda into
the vinegar
7. Observe
8. Record the mass of the contents of the
beakers. (Both beakers should stay on
balance)
Initial
Mass
21.4 g
Final Mass
20.9 g
Change in
Mass
-0.2 g
What is a chemical reaction?
• A process in which substances are changed
into new substances
– Ex. Water (H2O) can break apart to form
Hydrogen and Oxygen
Describe what happens when the
vinegar was poured into the cup of
baking soda.
• Lots of bubbles
• Produced a gas
– Bag got bigger
• Fizzed
• Solution became cold
Is this a chemical reaction? What
evidence do you have to support your
answer?
• Yes
• Evidence
– Bubbles / Gas was produced
The gas produced in this reaction can
put out fires. It is also a gas used by
plants. Make an educated guess about
its identity.
• Carbon Dioxide
How does the change of mass from
the plastic bag relate to the change of
mass from the beaker?
• The change of mass in the Plastic Bag should
have been less than the change of mass in the
Beaker
Why do you think the changes in mass
are different?
• The plastic bag trapped the Carbon Dioxide
gas that was produced (bag got larger) so
mass wasn’t lost.
• In the beaker the gas wasn’t trapped and
could’ve been lost.
What is the conservation of mass?
• Matter is not created or destroyed
• Reactants mass will equal the products mass
Which set up demonstrates the
conservation of mass more accurately?
• Plastic Bag
– The mass before the substances were mixed in the
plastic bag was equal to (or very similar to) the
mass after they were mixed because everything
stayed in the sealed bag
What experimental errors are
associated with this lab? List at least 3.
• Not sealing the bag
• Different amounts of baking soda and vinegar
• Incorrectly measuring the mass
– Pressing Zero too many times
• Using different scales
• Spilling
• The entire bag wasn’t on the scale