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Activity 25: Conservation of Mass

Activity 25: Conservation of Mass. Read B-64. Challenge: How does the total mass of the reactants compare to the total mass of the products in a chemical reaction?. Procedure. Follow procedure on pgs. B-65 to B-66. Data/Evidence:. Student Sheet 25.1.

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Activity 25: Conservation of Mass

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  1. Activity 25: Conservation of Mass

  2. Read B-64 • Challenge: How does the total mass of the reactants compare to the total mass of the products in a chemical reaction?

  3. Procedure • Follow procedure on pgs. B-65 to B-66

  4. Data/Evidence: • Student Sheet 25.1

  5. Which system is a closed system, and which is an open system? • Open System: the contents of the jar can mix with the air surrounding the outside of the jar. • Closed System: the chemical reaction is contained inside of the jar - all reactants and products stay in the jar. • Today, it is not an absolutely closed system - some heat and light will be able to escape.

  6. Can of Soda • When it is sealed, it is a closed system. • When it is opened and the gases are released it is an open system with the air around the can.

  7. What type of system is a person - open or closed? • Open System - we take in food, oxygen, and water, from outside our bodies and excrete waste, carbon dioxide, and other substances. • In reality, there are very few absolutely closed systems in our universe. • Our planet, for example, is an open system in that it exchanges mass with the solar system and galaxy.

  8. What is mass? • How much matter is in something. • The greater the mass, the more of the substance you have.

  9. Chemical Reactions • Signs of a Chemical Reaction: • Change in Color of Products • Production of Gas • Emission of Light or Heat • Appearance of a New Solid (Precipitate) or Liquid. • These changes in physical appearance or characteristics of the reactants are a way to visually detect a chemical change. • Change at the atomic level is not visible directly.

  10. Demonstration: Open System • 1 mL of copper chloride solution and 1 aluminum washer in the bottle. • What do you think will happen to the mass of the system - the bottle and reactants - as the reaction occurs? • Will it increase, decrease, or stay the same?

  11. Exothermic Reaction • Releases energy as the reactants interact chemically. • This is felt as heat. • Other exothermic reactions: • Combustion (Burning) and Rusting (Oxidation). • Do not grip your reaction chambers while conducting the reactions in closed systems.

  12. What evidence have you observed that indicates a chemical reaction occurred? • Formation of a new solid • Formation of bubbles • Change in color of the solution • Heat generated • What happened to the mass?

  13. You will also… • Conduct a second reaction with 1 mL 100,000 ppm copper chloride solution and 4 mLs of sodium hydrogen phosphate solution. • The reaction will be complete in approximately two minutes.

  14. Lab: Closed System • Use the balances carefully - be accurate! • Fix the lid onto the jar before beginning the reaction. • Place the reaction chamber on the table - do not keep it on the balance. • Do not let the substances mix before you have done the initial measurement of mass. • Press your thumbs against the lids while inverting the container to start the reactions. • Record detailed observations - how do you know a reaction occurred?

  15. Discussion • Record change-in-mass calculations • What trend do you see in the data? • What is this telling us about what is happening to the mass of the reactants as compared to the mass of the products? • What could explain why the mass may have changed? • How can we reduce error in this activity?

  16. Law of Conservation of Mass • Mass cannot be created or destroyed in a chemical reaction, but it can change form. • Mass stays the same in an open system and a closed system, but in an open system, the gas can escape. • Toxic substances that will have negative effects on humans, animals, or the environment, will still be present after a chemical reaction.

  17. Analysis Question #2 • The Law of Conservation of Mass goes against our perception of what we experience every day. • When we observe food cooking or wood burning, it appears that mass is lost. • This is because one of the products formed in these reactions is a gas we cannot see. • If we could collect all of the gas and water produced when cooking or burning, we would find that mass is conserved.

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