Pre-Lab 17B: Conservation of Mass

Purpose A French chemist named Antoine Lavoisier was the first to prove the law of conservation of mass. This law says that the total mass of the reactants in a chemical reaction is always equal to the total mass of the products. This is not as easy to see as you might think! As you do this investigation, you will discover how tricky it is to show the law of conservation of mass.

Key Question How do scientists describe what happens in a chemical reaction?

Background Define: law of conservation of mass closed system hypothesis

Drawing Draw this:

Work w/ one partner only; two parts to the lab Section 1: The purpose is to find the change in mass of the rxn w/ the effervescent tablet and fill in the data chart. Note the directions are in the data chart: -MUST zero balance (?) -what is the resolution of our balances? -OMIT STEPS 1 AND 2 -step 3: initial mass: do NOT add tablet to cup yet, also find the mass w/ tablet outside of cup (only one chance/tablet)

-step 4: while tablet is in the liquid, record qualifiable (?) observations -step 5: final mass: tap cup to release bubbles before you take final mass, why? - step 6: delta mass: find the difference btwn the two masses: : initial mass – final mass = mass difference why do we want this #?

Section 3: You write the chemical reaction and MUST show me/sign-off the tiles of the rxn

Sections 5 and 6 (note format change!!!!): your lab write-up must have these 6 labeled sections: 1) Purpose: to prove the law of conservation of mass 2) Hypothesis: You must make a hypothesis using this format: if…then…because 3) Materials: List the materials you will need in the experiment 4) Procedure: List the steps in the order you will follow in the experiment Working with your lab partners, devise an experiment which will prove that mass is conserved in the reaction of the tablet and water -Before you begin your experiment, approval from your teacher is required: signed-off -If your experiment does not work, DO NOT TRY AGAIN (this is a change from lab book) 5) Data: Record your data, in what?: quantitative (?) and qualitative (?) 6) Conclusion: a. use your data to describe why your hypothesis was right or wrong b. describe possible sources of error, be specific

Post Lab 17B: Conservation of Mass

Purpose A French chemist named Antoine Lavoisier was the first to prove the law of conservation of mass. This law says that the total mass of the reactants in a chemical reaction is always equal to the total mass of the products. This is not as easy to see as you might think! As you do this investigation, you will discover how tricky it is to show the law of conservation of mass.

Key Question How do scientists describe what happens in a chemical reaction?

Background Define: law of conservation of mass closed system hypothesis

Section 2: Does this experiment agree with the law of conservation of mass? b. Explain why you observed a difference in mass. Where did the missing mass go? Did it really disappear?

Section 6: What was your hypothesis? What was your expt setup and how did it differ from the first expt? What was your conclusion?