Cu (s) Cu 2+ (aq) Cu(OH) 2 (s) CuO (s) Cu 2+ (aq) Cu (s)

Transcription

1 Cycle of Copper Reactions Lab Exercise The following is a protocol for the multi-step transformation of copper metal based upon the following chemical transformations: Cu (s) Cu 2+ (aq) Cu(OH) 2 (s) CuO (s) Cu 2+ (aq) Cu (s) (1) Cu (s) + 4 H + (aq) + 2 NO 3 - (aq) Cu 2+ (aq) + 2 NO 2 (g) + 2 H 2 O (l) (2) Cu 2+ (aq) + 2 OH - (aq) Cu(OH) 2 (s) (3) Cu(OH) 2 (s) + heat CuO (s) + H 2 O (g) (4) CuO (s) + 2 H + (aq) Cu 2+ (aq) + H 2 O (l) (5) 3 Cu 2+ (aq) + 2 Al (s) 3 Cu (s) + 2 Al 3+ (aq) Materials: copper wire 12.0 M HNO3 (nitric acid) 6.0 M H2SO4 (sulfuric acid) 3.0 M NaOH (sodium hydroxide) concentrated HCl (hydrochloric acid) distilled water aluminum foil graduated cylinders (25 and 100 ml) glass boiling beads glass stirring rod balance accurate to 0.01 g microwave oven 250 ml Pyrex beakers 100 ml Pyrex beakers watchglass ring stand and iron ring with clamp funnel fast flow filter paper litmus paper graduated pipets (5 or 10 ml) with bulbs Procedure: **Safety Note: Goggles and lab aprons must be worn at all times while in the lab. Nonlatex or nitrile gloves must be worn whenever handling chemicals. Be very careful when transferring acids or bases from their containers into your glassware. *Note: All observations should be carefully recorded in your lab data packet.

2 First Reaction: Cu (s) + 4 H + (aq) + 2 NO3 - (aq) Cu 2+ (aq) + 2 NO2 (g) + 2 H2O (l) 1. Mass the piece of copper wire and record its mass to the nearest 0.01g. 2. Cut the wire into smaller pieces, being careful not to lose any. Place into a clean, dry 250 ml beaker. Note: Next steps must be performed in the fume hood by an instructor. 3. As instructor performs the next steps; record your observations in your lab packet. 4. The instructor will add 3 5 ml of concentrated nitric acid to the copper wire. 5. Reaction 1 will take place. 6. When the copper has all reacted, approximately 10 ml of distilled water will be added to the beaker. The following should be performed while waiting for your turn at the hood, or before beginning step 5: In your lab packet, using the mass of copper that you measured, calculate the number of moles of copper that you placed into the beaker. Second Reaction: Cu 2+ (aq) + 2 OH - (aq) Cu(OH)2 (s) 7. Using a pipet and pipet filler, add 15 ml of 3.0 M NaOH to the solution in the beaker. Gently stir the solution with a stirring rod. 8. Test the acidity/alkalinity of the solution using litmus paper. DO NOT PUT THE LITMUS PAPER INTO THE SOLUTION. Using the stirring rod, place 1 drop of solution onto a piece of litmus paper that has been placed onto a paper towel. 9. If the solution is acidic, add additional NaOH a few drops at a time, with stirring. Retest the solution with litmus paper after each addition of NaOH. Repeat the addition of NaOH until your solution is slightly basic. Recap NaOH bottle after completing this step. Third Reaction: Cu(OH)2 (s) + heat CuO (s) + H2O (g) **Note: Use hot hands mitts when handling hot beaker in microwave**

3 10. Dilute the solution by adding 80 ml of distilled H2O (use graduated cylinder to measure) to the beaker and stir. 11. Add two or three boiling beads to the beaker and cover the beaker with a watch glass. In microwave oven, heat the covered beaker for 20-seconds. Remove from the oven and stir. 12. Heat for another 20 seconds, then stir. 13. Repeat step Allow the solution to rest for a minute. Stir. If there is still any blue color visible, heat for a fourth time, but only for 10 seconds. Stir again. If the solution still looks blue, speak to an instructor and ask for assistance. 15. CuO forms as a solid black precipitate. Fill in appropriate data in lab packet. 16. Prepare the funnel by folding filter paper as demonstrated. Set up a ring stand with an iron ring and clamp. Place an empty, clean, 250 ml beaker under the ring and place funnel in iron ring so that the funnel will drain into the beaker. Place filter paper in funnel and wet with distilled water using a wash-bottle. 17. Filter the solution by stirring the CuO mixture and slowly pouring into funnel. Be sure to allow sufficient time for the funnel to drain, to avoid overflow. Always allow at least 1 cm of space between top of funnel and the level of CuO mixture. Do not try to remove the boiling beads. 18. Rinse beaker with distilled water and transfer any remaining solid into the funnel. 19. Measure approximately 30 ml of distilled water into the 250 ml beaker. 20. Add 2 boiling beads and cover the beaker with a watch glass. Place the beaker in the microwave, and heat the water for 20 seconds. 21. Rinse the residue in the funnel three times with 10 ml aliquots of warmed distilled water (using pipet), allowing the water to drain through the filter before adding additional water. 22. Keep filtered product, recover the boiling beads into a used beaker, and discard filtrate in waste container that is in the hood, as per instructor s directions. Record your observations. Fourth Reaction: CuO (s) + 2 H + (aq) Cu 2+ (aq) + H 2 O (l)

4 23. Place a clean, dry 250 ml beaker under funnel. Add 10 ml of 6 M H2SO4 drop-wise to the CuO in the funnel. Recap H2SO4 bottle after completing this step. If any solid remains on the filter paper, use the dropper to take the filtrate out of the beaker and put it back into the funnel. Note the details of the reaction in your lab packet. 24. Using the distilled water bottle, wash the filter paper in the funnel with small amounts of distilled water until no more blue is visible in the paper. Catch the filtrate in the beaker containing the copper solution. Fifth Reaction: 3 Cu 2+ (aq) + 2 Al (s) 3 Cu (s) + 2 Al 3+ (aq) 25. Using the provided chemical equations, determine the mass of aluminum foil that will be needed for reaction (see data sheet for details). 26. Measure needed mass of aluminum foil using the balance. Record the mass in your lab packet. Note: Next step must be performed in fume hood. **Wear gloves when handling concentrated HCl (and of course, your goggles)** 27. Add about half of the aluminum foil pieces to the solution in beaker. 28. The instructor will add a few drops of concentrated HCl to the beaker. Stir slowly with a glass rod while observing what happens to the aluminum foil. Record observations in lab packet. 29. When the evolution of gas stops, if solution is still blue, add more aluminum foil and a few more drops of concentrated HCl. 30. Fold a new piece of filter paper into cone shape as done previously. Determine the mass of the filter paper and record it in your data packet. 31. Write your initials on the filter paper using the permanent marker pen. Place paper in funnel and wet with some distilled water. 32. When reaction has come to completion (no evolution of gas and no more aluminum foil present), filter out product using a funnel and remember to put a beaker in place to catch the filtrate. 33. After product is filtered out, use the pipet to wash it with 20 ml of distilled water in small increments. Discard the filtrate in the appropriate waste disposal container.

5 34. Allow product to dry in a glass evaporating dish, using the drying oven as needed. 35. Determine mass of product and filter paper and record the mass in your data packet. 36. Calculate the percent yield for the series of reactions, as instructed in your data packet. Clean all glassware and return it to your station. Dispose of gloves as instructed before leaving the lab. Wash your hands before leaving the lab room.

6 Name: Cycle of Copper Reactions Data Packet The purpose of the data packet is to allow you to keep track of the essential data for the experiment. When directed to, enter data from lab experiment in the appropriate places. First Reaction: Initial mass of copper (to nearest 0.01 g): Record your observations of the first reaction: Calculate the number of moles of copper that reacted with nitric acid. Second Reaction: What color was the litmus paper when tested with the first sample of the copper solution? Approximately how much NaOH did you add to the solution before it tested basic with litmus paper? Third Reaction: Total time heated in microwave: Describe the transformation of copper hydroxide to copper oxide: Describe the characteristics of the copper oxide product:

7 Fourth Reaction: Volume of sulfuric acid used to dissolve CuO: Describe what happens when the acid is added to the copper oxide in the funnel: Fifth Reaction: Show how you determined the mass of aluminum foil needed for the reaction here: Measured mass of aluminum foil used: Describe your observations of the reaction here: Mass of filter paper: Final mass of copper product and filter paper: Mass of copper product:

8 Describe appearance of recovered copper product: Percent yield (recovery) of copper (show work): Suggest some sources of error. What might have led to the loss of some product or the unexpected gain of mass?