1. Lavoisier’s Experiments Conservation of Mass

2. Starter Question If I burn magnesium in air, what do you think will happen to its mass, will it increase, decrease, or stay the same? What if I burn wood? Why do you think this will happen? If I burn magnesium in air, what do you think will happen to its mass, will it increase, decrease, or stay the same? What if I burn wood? Why do you think this will happen?

3. Lavoisier Tax collector Tax collector Very precise Very precise Experiments with mercury Experiments with mercury

4. Mercury Experiment Two observations: Two observations: - red crystals - decrease in volume of air Did further tests Did further tests

5. Tests on the Air Put out flames Put out flames Didn’t react with limewater Didn’t react with limewater - no CO 2 Killed animals Killed animals Conclusion: Hg had reacted with “more respirable” part of the air Conclusion: Hg had reacted with “more respirable” part of the air

6. Red Crystals “carefully collected the 45 grains” “carefully collected the 45 grains” recovered the air recovered the air recombined it with the other part recombined it with the other part same properties as before experiment same properties as before experiment further tests with animal respiration further tests with animal respiration

7. Crystal Reaction Conclusions 1/5 of the air “respirable” (oxygen) 1/5 of the air “respirable” (oxygen) 5/6 “mephitic” or “nitrous state” (nitrogen) 5/6 “mephitic” or “nitrous state” (nitrogen) “aerial chalky acid” released in respiration (carbon dioxide) “aerial chalky acid” released in respiration (carbon dioxide)

8. What’s Going on? His initial reaction: His initial reaction: mercury + oxygen (from air)  mercury(II) oxide 2Hg (l) + O 2 (g)  2HgO (s) Precision enabled him to account for all the components as masses Precision enabled him to account for all the components as masses

9. What does it mean? total mass of reactants = total mass of products total mass of reactants = total mass of products atoms are not lost or gained, just rearranged into new compounds with different bonds atoms are not lost or gained, just rearranged into new compounds with different bonds We should balance our equations to reflect this! Hg (l) + O 2 (g)  HgO (s) 2Hg (l) + O 2 (g)  2HgO (s)

10. Back to the Questions If I burn magnesium in air, what do you think will happen to its mass? If I burn magnesium in air, what do you think will happen to its mass? magnesium oxide (s) Increase, but in closed container stays the same! What if I burn wood? What if I burn wood? carbon dioxide (g) Decrease, but in closed container stays the same! Closed vs open container – we trap the gasses so we can account for their changes in the calculation!

11. Lab Experiment on page 168 of your text Experiment on page 168 of your text Marked on accuracy and clarity of your lab notes! Record: - Details of experiment set-up + conditions - Observations during the reaction - Masses before and after - Any other relevant/weird/interesting observations

12. Lab Procedure: Procedure: 1) Read through pg 168 first 2) Do lab on pg 168, answer questions, & record observations 3) Complete model activity as a group 4) Before you leave: hand in lab notes and pick up marked quizzes and homework sheets.