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! 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 g40.02 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 g2.01 g
Lab Summary Plastic Bag Beaker Initial MassFinal Mass Change in Mass 22.9 g22.7g-0.2 g Initial MassFinal Mass Change in Mass 21.4 g20.9g-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 (H 2 O) 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