1. Some Things Never Change
Conservation of Mass

2. Chem Catalyst Examine the following reaction:
Na2CO3(aq) + CaCl2(aq) NaCl(aq) + CaCO3(s)
Describe what you will observe when sodium carbonate, Na2CO3(aq), and calcium chloride, CaCl2(aq), are mixed.
Will the mass increase, decrease, or stay the same after mixing? Explain?

3. Pre-lab Predictions
Our purpose: to explore the evidence for the law of conservation of mass.
Make mass predictions

4. Pre-Lab Preview the lab procedure and data tables. Questions?
Tare weight: Mass your 2 dry beakers together before you start. Subtract this from all of your masses.
Dispose of products in waste bin, rinse and dry your beakers after each reaction.
If you are a team of 2 or 3, work all together. If you are a team of 4 or 5, split in 2. Second group weighs at central weigh station.

5. Safety? Goggles & Lab aprons Hair up Feet covered
Move with caution!!!!!!!!

6. Discussion Which changes were physical? Which changes were chemical?
What happens to atoms when a substance goes through a physical change?
What happens to atoms when a substance goes through a chemical change?
Was anything added to or removed from the cups during any of the chemical reactions?
If you were to collect all the gas that escaped from the third reaction, what do you think you’d find?

7. Let’s Test
Demonstration:
Mg(s) + 2HCl(l) MgCl2(aq) + H2(g)

8. Check-In Consider the reaction: CuCO3(s) + H2SO4(aq) CO2(g) + CuSO4(l)
What will you observe when these substances are combined?
Will the mass increase, decrease or stay the same? Explain why.

9. Homework
Read the Toxins Lesson 4: Some Things Never Change, pages
Do questions 1-7.