Conservation of Matter

Chemical Reactions

• Happen all of the time• Happen naturally or can be man made• Can be physical or chemical

PHYSICAL

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 = Product

Mass of Reactants

Mass of Products

Example: Tin Fluoride

• Tin + hydrogen fluoride -> tin fluoride + hydrogen

• What’s the total mass of the reactants?– 158.72 g

• So what should the mass of the products be?– 158.72 g

118.7 g

40.02 g

• Tin + hydrogen fluoride -> tin fluoride + hydrogen

• 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.

Total Mass of Reactants: 158.72 g

156.71 g

2.01 g

Lab Summary

• Plastic Bag

• Beaker

Initial Mass Final Mass Change in Mass

22.9 g 22.7g -0.2 g

Initial Mass Final Mass Change in Mass

21.4 g 20.9g -0.5 g

Plastic Bag Procedure1. 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. Observe8. 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 Mass22.9 g

Final Mass22.7g

Change in Mass-0.2 g

Beaker Procedure1. Place 2 beakers on the balance2. Press zero3. 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 vinegar7. Observe8. Record the mass of the contents of the

beakers. (Both beakers should stay on balance)

Initial Mass21.4 g

Final Mass20.9 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