Law of Conservation of Mass (LCM)

1. Law of Conservation of Mass (LCM)

2. Law of conservation of mass – states that mass is neither created nor destroyed during chemical reactions or physical changes

3. Reactant – substance that undergoes a reaction

4. Product – a new substance formed when reactants undergo chemical change

5. Balanced equation - An equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge are the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.

6. Coefficients – a number placed in front of the parts of a chemical equation to indicate how many are involved ; always a positive whole number.

7. Subscript –

8. Formula – a combination of chemical (element) symbols that show what elements make up a compound and the number of atoms of each element

9. Chemical equation - A symbolic representation of what happens when chemicals come in contact with one another.  A balanced chemical equation shows how many of what molecules react, how many of what molecules result, and sometimes the state of the substances.

10. Demo: LCM – in chemical reactions, you always end up with the same amount of stuff you start with. “Stuff” – very scientific could be atoms or mass.

11. Demo: What is the formula for aluminum chloride? What is the formula for copper chloride?

12. Demo: What will happen if I drop aluminum into a copper chloride solution?

13. Demo: Write the chemical reaction… CuCl2 + Al → AlCl3 + Cu Do you notice anything?!

14. Demo: Balance the chemical reaction… 3CuCl2 + Al → AlCl3 + Cu 3CuCl2 + Al → 2AlCl3 + Cu 3CuCl2 + Al → 2AlCl3 + 3Cu 3CuCl2 + 2Al → 2AlCl3 + 3Cu

16. __Ca(C2H3O2)2 + __K3PO4__Ca3(PO4)2 + __KC2H3O2Which set of coefficients balances the equation? A. 3, 3, 1, 2B. 6, 1, 1, 3C. 3, 2, 1, 6D. 6, 2, 1, 6 Each answer is on the following slide.

17. Which of these would support the idea that mass is conserved in a reaction that produces a gas as a product? A. Heating the reactants to ensure the reaction occurs in a gaseous stateB. Subtracting the mass of the gas from the mass of the solid and liquid productsC. Mixing the reactants and measuring their total mass D. Trapping the gas and measuring its mass C

18. Aluminum metal and oxygen gas combine to produce aluminum oxide (Al2O3). Which of these is the balanced equation for this reaction? A. Al + O2 Al2O3B. 2Al + 2O2 2Al2O3C. 2Al + 3O2 5Al2O3D. 4Al + 3O2 2Al2O3 D

19. CaCO3 CaO+ CO2 The chemical equation shows CaCO3 being heated. Which of these statements best describes the mass of the products if 100 g of CaCO3 is heated? A. The difference in the products’ masses is equal to the mass of the CaCO3. B. The sum of the products’ masses is less than the mass of the CaCO3. C. The mass of each product is equal to the mass of the CaCO3.D. The sum of the products’ masses equals the mass of the CaCO3. D

20. Which chemical equation supports the law of conservation of mass? A. 2H2O(l)  H2(g) + O2(g) B. Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g) C. Al4C3(s) + H2O(l)  CH4(g) + Al(OH)3(s) D. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) D

21. 2Cu + O22CuO When 127 g of copper reacts with 32 g of oxygen gas to form copper (II) oxide, no copper or oxygen is left over. How much copper (II) oxide is produced? A. 32 gB. 95 gC. 127 gD. 159 g D

22. K + H2O  KOH + H2What is the coefficient for H2O when the above equation is balanced? A. 1 B. 2C. 3D. 4 D

23. According to the law of conservation of mass, how much zinc was present in the zinc carbonate? A. 40 gB. 88 gC. 104 gD. 256 g B

24. What are the coefficients that will balance this chemical equation? A. 2, 1, 1B. 3, 4, 2C. 2, 2, 1D. 4, 3, 2 C

25. The illustrations show a conservation-of-mass experiment. The solution in the beaker lost mass because _____. A. materials have less mass at high temperaturesB. the mass of the reactants and products was less than 100 gC. sodium sulfate (Na2SO4) is lighter than airD. some of the water molecules turned into gas C

26. D