Lavoisier’s Experiments Lavoisier’s Experiments

Conservation of Mass Conservation of Mass

Starter Question Starter Question

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

Lavoisier Lavoisier

Tax collectorTax collector Very precise Very precise Experiments with Experiments with

mercury mercury

Mercury Experiment Mercury Experiment

Two observations: Two observations:

- red crystals- red crystals

- decrease in volume - decrease in volume of air of air

Did further testsDid further tests

Tests on the Air Tests on the Air

Put out flames Put out flames Didn’t react with limewater Didn’t react with limewater

- no CO- no CO22 Killed animals Killed animals

Conclusion: Hg had reacted with Conclusion: Hg had reacted with “more respirable” part of the air “more respirable” part of the air

Red Crystals 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 same properties as before

experiment experiment further tests with animal respiration further tests with animal respiration

Crystal Reaction Conclusions Crystal Reaction Conclusions

1/5 of the air “respirable” (oxygen)1/5 of the air “respirable” (oxygen)

5/6 “mephitic” or “nitrous state” 5/6 “mephitic” or “nitrous state” (nitrogen)(nitrogen)

““aerial chalky acid” released in aerial chalky acid” released in respiration (carbon dioxide) respiration (carbon dioxide)

What’s Going on? What’s Going on?

His initial reaction: His initial reaction:

mercury + oxygen (from air) mercury + oxygen (from air) mercury(II) mercury(II) oxide oxide

2Hg2Hg(l)(l) + O + O22(g)(g) 2HgO 2HgO(s)(s)

Precision enabled him to account for Precision enabled him to account for all the components as massesall the components as masses

What does it mean? What does it mean? total mass of reactants = total mass of total mass of reactants = total mass of

productsproducts

atoms are not lost or gained, just atoms are not lost or gained, just rearrangedrearranged into new compounds with into new compounds with different bondsdifferent bonds

We should balance our equations to reflect We should balance our equations to reflect this! this!

HgHg(l)(l) + O + O22(g)(g) HgO HgO(s)(s)

2Hg2Hg(l)(l) + O + O22(g)(g) 2HgO 2HgO(s)(s)

Back to the QuestionsBack to the Questions If I burn magnesium in air, what do you If I burn magnesium in air, what do you

think will happen to its mass? think will happen to its mass? magnesium oxide (s)magnesium oxide (s)

Increase, but in closed container stays the same! Increase, but in closed container stays the same!

What if I burn wood? What if I burn wood? carbon dioxide (g)carbon dioxide (g)

Decrease, but in closed container stays the same! Decrease, but in closed container stays the same!

Closed vs open container – we trap the gasses so we can Closed vs open container – we trap the gasses so we can account foraccount for

their changes in the calculation!their changes in the calculation!

Lab Lab Experiment on page 168 of your text Experiment on page 168 of your text

Marked on accuracy and clarity of your lab Marked on accuracy and clarity of your lab notes! notes!

Record: Record: - Details of experiment set-up + conditions Details of experiment set-up + conditions - Observations during the reaction Observations during the reaction - Masses before and after Masses before and after - Any other relevant/weird/interesting Any other relevant/weird/interesting

observationsobservations

Lab Lab

Procedure: Procedure:

1)1) Read through pg 168 first Read through pg 168 first

2)2) Do lab on pg 168, answer questions, & Do lab on pg 168, answer questions, & record observations record observations

3)3) Complete model activity as a group Complete model activity as a group

4)4) Before you leave:Before you leave: hand in lab notes hand in lab notes and pick up marked quizzes and and pick up marked quizzes and homework sheets. homework sheets.