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Law of Conservation of Mass Antoine Lavoisier, ~ 1775

Law of Conservation of Mass Antoine Lavoisier, ~ 1775. Law of Definite Proportions J.L. Proust, 1799. Law of Conservation of Mass. In a chemical reaction, the Law of Conservation of Mass states that the Mass of the Reactants must equal the Mass of the Products. C + D + E.

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Law of Conservation of Mass Antoine Lavoisier, ~ 1775

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  1. Law of Conservation of Mass Antoine Lavoisier, ~ 1775 Law of Definite Proportions J.L. Proust, 1799

  2. Law of Conservation of Mass In a chemical reaction, the Law of Conservation of Mass states that the Mass of the Reactants must equal the Mass of the Products. C + D + E A + B Products Reactants Mass A + Mass B = Mass ( C + D + E )

  3. Law of Definite Proportions Any pure compound only contains the same elements in the same proportion by mass. H2O Define proportion: the ratio that relates one part to another part, or relates one part to the whole. Example: A large proportion of the people present in this classroom are students.

  4. Acids • Vinegar is an Acid • Chemical name is Acetic Acid • Chemical formula: CH3CO2H

  5. Bases • Baking Soda is a Base • Chemical name is Sodium Bicarbonate • Chemical formula: NaHCO3

  6. Acids React with Bases = = =

  7. Hypothesis • If reactant is 84 grams of baking soda, then by proportion, a product is 44 g of carbon dioxide. NaHCO3+ CH3CO2H + 84g 60g = 144g H2O+ CH3CO2Na + CO2 Water Sodium Acetate Carbon Dioxide 18g + 82g + 44g = 144g

  8. Law of Definite ProportionsCalculating Mass of Molecule A

  9. Law of Definite ProportionsCalculating Mass of Molecule B

  10. Law of Definite ProportionsCalculating Mass of Molecule B

  11. Law of Definite ProportionsCalculating Mass of Molecule C

  12. Law of Definite ProportionsCalculating Mass of Molecule C

  13. Law of Definite ProportionsCalculating Mass of Molecule D

  14. Law of Definite ProportionsCalculating Mass of Molecule E

  15. Law of Definite ProportionsCalculating Mass of Molecule E

  16. Mass Reactants = Mass Products Reactants 14 atoms Mass of 6 atoms Mass of 8 atoms NaHCO3+ CH3CO2H + 84g 60g = 144g H2O+ CH3CO2Na + CO2 Water Sodium Acetate Carbon Dioxide = 144g 18g + 82g + 44g Mass of 3 atoms Mass of 8 atoms Mass of 3 atoms Products 14 atoms

  17. Test Hypothesis To shorten the reaction time, we want to use only a small amount of baking soda. • If reactant is 84 grams of baking soda, then we would get 44 grams of carbon dioxide. • But if we use only 5 grams of baking soda, then by proportion, the product is 2.6 grams of carbon dioxide. 5g Sodium Bicarbonate ?g CO2 5g x 44g = 2.6g CO2 84g

  18. How can we measurethe mass of gas produced? • Subtract the mass of the bottle + cap afterthe gas is released from the mass of the bottle + cap before the CO2is released. The value should less than 2.6 g because about 10% of the CO2 remains dissolved in the water solution.

  19. How do we Measurethe Volume of a Gas? • If we can measure the circumference of a sphere that traps the gas, such as a balloon, then we can calculate the volume of the gas.

  20. Volume Calculation • What is the volume of 2.6 grams of CO2? • The density of CO2 is 0.001975 g/cm3 V = m d V = 2.6g 0.001975g/cm3 V = 1,316 cm3

  21. Circumference Calculation • What should be the circumference of the balloon, if it holds 1,316 cm3 of CO2? V = C3 where C = Circumference 6π2 V6π2 = C3 1,316 cm3 x 6 (3.1415 x 3.1415) = C3 42.7 cm = C

  22. How do I Calculatethe Mass of a Gas? • If we can measure the volume of the gas and we know its density, then we use D = m/V: Density (D) = Mass (m) Volume (V) or Volume (V) x Density (D) = Mass (m)

  23. Comparing Our Measurements with Our Calculations • Calculated Circumference: 42.7 cm • Measured Circumference: • Explain Any Difference

  24. Conclusion My hypothesis……. was supported by my data because the mass of all the products of this chemical reaction was equal to mass of all the reactants

  25. Conclusion Continued I know that this reaction obeys the Law of Conservation of Mass because I used the Law of Definite Proportions to predict the mass of carbon dioxide, and my results matched my prediction within the +/- margin of uncertainty caused by the carbon dioxide that remains dissolved in the water.

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