QOD #41
• Name one chemical PROPERTY and give an
example of a chemical change that could
happen because of that property.
• Name one physical PROPERTY and give an
example of a physical change that could happen
because of that property.
Law of Conservation of
Mass
The Law of Conservation
of Mass - The mass stays
the same before and after a
physical change.
(Pizza Dough)
Making Lemonade – Proving Conservation
of Mass
Materials:
• Large clear cup
• Dixie cup with lemonade mix
• Water
• Spoon
• Mass scale
DON’T THROW AWAY ANY OF MY CUPS OR
SPOONS.
Procedures:
1. Fill up the cup with water ¾ full.
2. Pour in the mix, but do not stir!
3. Measure the mass of the cup of water mix
and record the mass.
4. Mix the ingredients together and stir with
spoon.
5. Measure the mass of the ingredients after
the physical change.
6. Drink lemonade!!
7. Clean up, then answer questions.
Data Table:
Mass Before Physical Change
Total mass of cup of water +
lemonade mix before stirring
_____________ grams
Mass After Physical Change
Total mass of cup of lemonade
after stirring _________ grams
Questions (RAP answers)
1. What happened to the mass before
and after the physical change?
2. Why did that happen?
3. Why is dissolving a physical change?
Clean Up Procedures
1. Place small dixie cup back on tray where you
found it.
2. Rinse out clear cup with water and place on tray
in the front of the class.
3. Rinse off spoon with water and place in cup of
spoons.
QOD #42
•Ms. Rathjen’s room is so cold
that her bottle of water froze on
her desk. If the mass of the
water and bottle was 250 grams
before the physical change, what
was it after?
The Law of Conservation
of Mass (in a chemical
change) - The mass stays
the same before and after a
chemical change in a closed
system.
Chemical Change– Proving Conservation
of Mass
Materials:
• Baking Soda
• Water bottle
• Balloon
• Vinegar
• Mass scale
DON’T THROW AWAY ANY MATERIALS! Be
careful with balloons!
Procedures:
1. Get a water bottle partially filled with vinegar.
2. Put a spoonful of baking soda in the balloon with a
partner.
3. Find the mass of the balloon with baking soda and the
bottle with vinegar before mixing them.
4. Place the balloon over the mouth of the water bottle
and shake the balloon until all the baking soda falls
into the vinegar. Hold the balloon onto the bottle!
5. After the chemical change has taken place, find the
mass of the bottle and balloon (without removing the
balloon from the bottle). Record data.
6. Write down qualitative observations and draw
diagram.
7. Clean up, then answer questions.
Data Table:
Mass Before Chemical
Change
Bottle of vinegar +
balloon_____
Qualitative Data:
Diagram: (Label picture)
Mass After Chemical
Change
Total mass of bottle with
the balloon ______
Questions (PQPA answers)
1. What happened to the mass before and after the
chemical change? Why did that happen?
2. Why is it necessary to have a closed system for the
Law of Conservation of Mass to apply to a chemical
change?
3. Why was this reaction considered a chemical
change?
The chemical equation for the overall reaction is:
NaHCO3(s) + CH3COOH(l) → CO2(g) + H2O(l) +
Na+(aq) + CH3COO-(aq)
with s = solid, l = liquid, g = gas,
aq = aqueous or in water solution
Another common way to write this reaction is:
NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O +
CO2
10-5-12
QOD#20
Tommy wants to see what happens to the mass of
his milk as it sours in the refrigerator. The mass of
the milk is 400 g before it goes bad.
(Fill in the blanks below)
1. The mass after the change is ______.
2. I know this because _______.
3. This is a ________ change because _______.