Conservation of Mass in Chemical Reactions Lab Name: 5 th Grade PSI Science Score: / 5 Experiment Question: What happens to the total mass of substances when a chemical reaction occurs? Hypothesis Starters: 1. Define the term Conservation of Mass. 2. Define the term chemical reaction. 3. What are some common signs of chemical reactions? Purpose: In this experiment, you will explore what happens to the total mass of a solution when a chemical reaction occurs. During a chemical reaction, starting chemicals come into contact to form products with different physical properties. They may have a different color or may change from a liquid to a solid. One technique chemists often use to help substances react is to dissolve them in water first. This allows the pieces to move around and react more easily. Even though new substances are made, Conservation of Mass is still true. Sometimes this is tricky to show like when you burn a match or a candle. Some of the products are gases like carbon dioxide which often just float away and mix with the air. These gases have mass which counts but since they float away, they do not get measured. This makes Conservation of Mass seem like it isn t true. Any time it looks like Conservation of Mass is not true, look at your reaction and try to figure out where the extra mass came from or where it went.
Safety Flames will be used during this activity. Never hold a burning object with your hands. Always use tongs or place it in a fire-safe dish and let it burn there. Goggles and aprons should be worn at all times. Materials The materials and directions for each station are included individually. Complete each station before moving on to the next station. There are extra station spaces at the end for you to write in stations that you have created or that your teacher has created for you in addition to the standard stations. Station One: Magnesium Ribbon Materials: Ceramic dish 2.5cm long piece of magnesium ribbon Wand style lighter balance or scale Directions: 1. Record the starting mass of the ceramic dish and the magnesium ribbon. 2. Record observations of the magnesium ribbon in its original state. 3. Ignite the magnesium ribbon with the lighter. 4. DO NOT look directly at the magnesium ribbon while it burns because it may damage your eyes. 5. Record observations of the magnesium ribbon after it has reacted. 6. Once the ceramic dish cools to room temperature, record the ending mass of the ceramic dish and the burned magnesium. 7. Clean up as instructed by your teacher. Observations Starting Mass Ending Mass Starting Observations Ending Observations
Station Two: Vinegar and Baking Soda Version 1 Materials: Balance or Scale Scrap Paper Vinegar Baking soda 50mL or 100mL Graduated Cylinder Directions: 1. Place the scrap paper on the balance. 2. Add about 1.0g of baking soda to the scrap paper 3. Add about 25.0mL of vinegar to the graduated cylinder 4. Place the graduated cylinder on the balance with the scrap paper and baking soda. 5. Record the starting mass of everything on the balance. 6. Record starting observations of everything on the balance. 7. Pour the baking soda into the graduated cylinder slowly so that it does not foam over the top. 8. Record observations of what happened during the reaction and what the chemicals look like after the reaction has stopped. 9. Place the scrap paper on top of the graduated cylinder. 10. Record the ending mass of everything on the balance. 11. Clean up as instructed by your teacher. Observations Starting Mass Ending Mass Starting Observations Ending Observations
Station Three: Vinegar and Baking Soda Version 2 Materials: Balance or Scale Balloon, log and skinny like for balloon animals Rubber band Vinegar Directions: Baking soda 10mL Graduated Cylinder 1. Place the empty balloon on the balance. 2. Add about 0.25g of baking soda to the balloon. 3. Shake all of the baking soda to the bottom of the balloon. 4. About 1.0cm above the baking soda in the balloon, twist the balloon 10 times to close off the baking soda from the rest of the balloon. 5. Fold the end of the balloon up and use the rubber band to make sure it does not accidentally unfold. 6. Add about 5.0mL of vinegar to the graduated cylinder 7. Add the vinegar to the balloon and carefully tie the end of the balloon closed. 8. Place the balloon with the rubber band on the balance. 9. Record the starting mass of everything on the balance. 10. Undo the rubber band. 11. Untwist the balloon so the vinegar and baking soda can react. 12. Once the reaction stops, place the balloon and rubber band on the balance. 13. Record the ending mass of everything on the balance. 14. Record observations of the reaction. 15. Place the graduated cylinder on the balance with the scrap paper and baking soda. 16. Record the starting mass of everything on the balance. 17. Record starting observations of everything on the balance. 18. Pour the baking soda into the graduated cylinder slowly so that it does not foam over the top. 19. Record observations of what happened during the reaction and what the chemicals look like after the reaction has stopped. 20. Clean up as instructed by your teacher. Observations Starting Mass Ending Mass Starting Observations Ending Observations
Station Four: Copper (II) Nitrate with Sodium Hydroxide Materials: Balance or Scale 2 Beakers Test tube with Copper (II) Nitrate solution Test tube with Sodium Hydroxide solution Directions: 1. Place one test tube in each beaker so they do not tip over or roll away. 2. Place everything on the balance. 3. Record the starting mass of everything. 4. Record observations of everything. 5. Take the beakers off of the balance. 6. Take the copper (II) nitrate test tube out of its beaker. 7. Pour the copper (II) nitrate solution into the empty beaker. 8. Place the empty test tube in the other beaker. 9. Pour the sodium hydroxide into the beaker with the copper (II) nitrate. 10. Place the empty test tube with the other test tube in the beaker. 11. Record observations of what happened when the solutions were mixed. 12. Place both beakers and their contents on the balance. 13. Record the ending mass of everything. 14. Clean up as instructed by your teacher. Observations Mass Before Mass After Observations Before Observations After
Materials: Custom Station Directions: Observations Before: Observations During: Observations After:
Laboratory Questions: On a sheet of paper or in your laboratory notebook, answer the following questions for each station you were able to test. 1. Was conservation of mass true at station one? Explain your thinking. 2. Was conservation of mass true at station two? Explain your thinking. 3. Was conservation of mass true at station three? Explain your thinking. 4. Was conservation of mass true at station four? Explain your thinking. 5. What purpose did the balloon serve at station three? Did it collect anything? Conclusion: On a sheet of paper or in your laboratory notebook, write a paragraph or two that summarizes the experiment results and covers the following key points. 1. How did you know that chemical reactions occurred at each station? 2. Was Conservation of Mass true at each station? If not, why not?
Notes to the Teacher: Be aware of your school s policy regarding latex balloons. Some schools do not permit their use because of latex allergies. Often, you may be granted permission if you perform it as a demonstration. This could be set up as a station experiment where the students perform each station or as a demonstration experiment where the teacher performs each for the class as a whole. You don t technically need to do all four stations. One station should illustrate the point if performed correctly. Station one can be easily done as a demo if fire safety is a concern. The extra mass comes from the oxygen in the air. This experiment disproves the idea of phlogiston. If your students are not familiar with phlogiston, you may wish to have them complete a quick research of it to show how scientific ideas are refined and corrected throughout history. Be sure to test the amounts listed in station three to make sure your balloons will not overinflate and pop. Adjust amounts if needed. Station four should have color changes and a precipitate that forms.