Experiment 3
The Stoichiometry and Reactions of Some Copper Compounds

PROCEDURES

1. Weigh a clean dry 250mL beaker and record the results on the data sheet (IV. Data).  Obtain copper turnings that weigh about 1.000g and add to the 250mL beaker.  Reweigh the beaker and record the mass of the beaker and copper.  Calculate the initial mass of the copper and record this mass on the data sheet.   

2. OPEN THE FUME HOOD at your station to carry out the dissolution.  With the beaker under the hood, carefully add 5mL of 15M (concentrated) HNO3.  The reaction produces toxic and noxious fumes of NO2.  Keep the beaker in the fume hood until the reaction is complete.  (NO2 is the dangerous component of brown smog.)  Record in the observations section (III. Observations and Chemical Equations) a complete description of what occurs. The chemical equation is complex and so is provided for you. (REACTION 1)

3. Now add distilled water to bring the total volume to about 150mL (roughly half full).  Describe what happens. Write a balanced chemical equation to describe what happens, the beginning is provided. (REACTION 2)

4. Add 8mL of 6M NaOH, slowly while stirring with a glass rod.  (Use the same glass stir rod throughout the experiment and do not remove from beaker, this will prevent material loss.) Record your observations and write a balanced chemical equation to describe what happens. (REACTION 3)

5. Assemble a ring stand, ring, wire gauze and Bunsen burner.  Put the beaker on the wire gauze and heat gently, stirring nearly continuously to prevent bumping.  Do not boil the solution, a gentle warming is all that is necessary.

6. The reaction takes 5-10 minutes to reach completion.  The change is complete when the solid is uniform in color and the solution is colorless.  Describe what happens and write a balanced chemical equation for the reaction. (REACTION 4)

7. Remove the beaker from the wire gauze and replace it with a clean beaker filled with 150mL of distilled water (no stirring rod).  Heat to just below boiling.

8. Allow the solution to settle.  Decant the supernatant solution (liquid on top).  The solution should be disposed of in a waste beaker (250mL beaker).  Be careful not to lose any of the solid CuO that is formed.

9. When the water is hot, turn off the Bunsen burner and pour the hot water into the beaker with the solid CuO.  Stir briskly, allow to settle, and decant the supernatant as before.  Avoid losing any of the solid.  This is a washing step which will remove any unreacted NaOH solution.

10. Add 30mL of 3M H2SO4 (CAUTION!) slowly and with stirring to the solid CuO.  Record your observations and write a balanced chemical equation for the reaction. (REACTION 5)

11. Weigh about 2.000g of 30-mesh zinc metal in a weigh boat or small beaker. Use THE HOOD for the next step. Add the zinc metal to the copper sulfate solution, a few pieces at a time.  Stir until the solution is colorless or nearly colorless.  A colorless solution indicates that all the copper ions have been removed from the solution.  Allow the reaction to continue until gas evolution ceases and then continue stirring for 2-5 minutes more.  Record all observations.  There are TWO reactions occurring, write the balanced chemical equation for each.  (REACTION 6) (REACTION 7)

12. Add 10mL of 6M HCl.  When the zinc has completely dissolved as evidenced by no further hydrogen gas evolution, decant the HCl solution from the solid copper.  The decantate should be discarded in the “acid/waste” container.  Wash the copper with two 50mL portions of distilled water, decanting the wash water between each washing.  The waste wash should be disposed of in the “acid/base” container.  Before performing the acetone wash, extinguish all flames!  Acetone is flammable.  Wash the precipitate with three 10mL portions of acetone, decanting the liquid after each individual wash.  Dispose of the acetone in the “acetone waste” container.  Record your observations.

13. Use a pencil to write your names on a piece of paper and place it in the beaker with the copper. Store the sample in the drying area designated by your instructor. You will determine the mass of copper recovered during the next lab period after your sample has dried. At that time, you will also submit your sample to your instructor for grading. The amount of copper recovered is dependent on your lab technique. You should be able to recover nearly all with which you started. Calculate the percent loss (or gain) of copper using the equation on page 61.

You will turn in your lab report at the conclusion of the first lab period. You will be able to complete nearly everything.  Your instructor will partially grade your lab report and return it to you to complete at the beginning of the next lab period when you will enter the data after drying your sample.