Round and round again….the mini-lifecycle of a gram of copper Introduction: You’ve completed a Lifecycle of a Material project and should understand the importance of the Law of Conservation of Matter. Its now time to unite these two ideas and follow copper atoms on their journey through several chemical processes. The final process will convert the copper back to its original form, therefore creating a cycle. Objectives: 1. Using omnigraffle, create a lifecycle of your copper based on chemical reactions conducted in class. 2. Classify chemical reactions. 2. Understand how to interpret a Materials Safety Data Sheet (MSDS). 3. Calculate percent yield and percent error to determine success of reactions. Part II. Retrieving Copper Safety: Look up the MSDS sheet for copper (II) oxide (CuO), hydrochloric acid (HCl), copper (II) chloride (CuCl2) and zinc at www.flinnsci.com. Note any safety precautions with this substance. Hotplates will be used again – be careful they can get hot! Goggles must be worn at all times. . Materials: Solution from Part IIA, zinc, watchglass, scoopula, forceps, 10 mL of 1M HCl solution (see teacher), filter paper, stirring rod with rubber policeman, pencil Procedure: Take pictures before, during and after. Part 2B: Converting Copper(II) Chloride (CuCl2) to Copper (Cu) The final step in this investigation is to convert the dissolved copper(II) chloride (CuCl2) to copper metal. To do this, you will add zinc metal to the solution of copper (II) chloride. Write a balanced equation for this reaction: CuCl2 (aq) + Zn (s) ZnCl2 (aq) + Cu (s) 1. Obtain a watch glass that can completely cover the top of the container containing copper(II) chloride (CuCl2) solution from Part IIA. Mass out the same amount of zinc metal as the amount of copper you started with. For example, if originally 1 gram of copper, than measure 1 gram of zinc. Add the zinc to the CuCl2 solution. See Figure 2.36. 2. Immediately cover the container with the watch glass, and allow it to stand for several minutes. Record your observations. 3. After the reaction has subsided, remove the watch glass and gently dislodge the solid copper that has formed on the surfaces of the zinc pieces. 4. Continue to dislodge the copper from the zinc until you are convinced that the zinc has stopped reacting with the solution. (How can you decide?) Then, add 10 mL of 1 M HCl to the beaker and carefully remove any large pieces of solid zinc from the beaker with forceps. Follow your teacher’s instructions for discarding the solid zinc. Replace the watch glass. Record your observations. 5. After a few minutes, carefully decant as much of the liquid as possible into an empty beaker. Follow your teacher’s instructions for discarding the liquid. 6. Wash the solid copper several times with distilled water. Decant the distilled water carefully – try not to lose any copper. 7. Transfer the copper to a labeled, pre-weighed piece of filter paper, and allow the copper to dry overnight. 8. After the sample and filter paper have dried, find the mass of copper metal. This represents the copper that you recovered from the copper(II) chloride solution. 9. Follow your teacher’s instructions for disposing of waste materials. Wash your hands thoroughly before leaving the laboratory. Figure 2.36 Pictures with observations: Before: During: After: Data Table Part 2B Data Mass(g) Mass of filter paper Mass of filter paper and copper residue Mass of copper residue 1. Adding HCl to CuO, in this lab, Retrieving Copper, resulted in the formation of a blue solution. This color is due to the presence of Cu2+(aq) ions. Consult your observations when answering the following questions: a. Describe what happened to the solution color after you added zinc (see Steps 9 and 10). b. What caused the changes you observed in the solution? c. How can the color of the solution be used to indicate when the zinc metal has removed the Cu2+ ions from the solution? 2. To recover Cu metal from the CuCl2 solution, you had to use other resources: a. What resources were “used up” in this recovery process? b. Where (to what location) did each resource finally go? 3. Percent Yield is a percentage reflecting how much copper made it through the cycle. The higher the number, the better the yield. Show calculations and final answer. % Yield = Final Mass Cu x 100 Original Mass Cu 4. Examine your percent yield. a. How much left the cycle? b. When did the atoms leave the cycle (provide 2 ways)? c. How could have you kept them in the cycle? Reflect on answer 4b. 5. How does this entire lab relate to a. the Lifecycle of a Material project? b. the Law of Conservation of Matter? Fully explain each connection. Assessments You’ve just taken copper through several chemical reactions. Complete the following as evidence that you understand this process. GROUP: (DUE Wednesday, December 23) 1. A lifecycle of the copper in this lab. See omnigraffle in teacher folder. 2. All three google docs (Part 1, Part 2A, Part 2B) 3. ALL WORKERS MUST BE EVIDENT IN GOOGLE DOC.
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