Work Sample 2

Justin Frost Copper cycle

Problem Statement: The purpose of this experiment was to use a series or laboratory techniques to prepare a "reaction cycle" for copper. This cycle takes copper through the stages of metallic copper, copper (II) hydroxide, copper (II) sulfate, and copper (II) nitrate and ends with a product that is pure copper. These compounds had to be experimentally tested to see what order would complete the copper cycle. Procedures: (1) Followed Procedures are included (pg. 265 handout) (2) Actual Procedures: A.

i. Acquire a 1 g (+ 0.001 g) sample of copper wire and record its mass ii. Put Cu wire in a small test tube. iii. Use dropper to add drops of HNO until no further reaction is visible **CAUTION: DO REACTIONS IN THE FUME HOOD *Gentle heating may be required to speed up the reaction.

B.

i. Use a dropper to add NaOH to your solution. Continuously stir and a precipitate should

form. ii. You can check the acidity with litmus paper every 10 drops and when litmus paper turns blue, stop adding drops (because solution is now basic). iii. Once a noticeable precipitate has formed, centrifuge the solution for 20 **CAUTION: MAKE SURE THAT CENTRIFUGE LID IS CLOSED THAT AN EMPTY "BALANCE" TEST TUBE IS PLACED SOLUTION IN THE CENTRIFUGE.

seconds.

SECURELY AND

ACROSS FROM YOUR

C.

i. Take test tube out of centrifuge. ii. Use a dropper pipette to decant the liquid (supernatant), leaving only the

precipitate in

the bottom of the test tube. iii. Add drops (about 10) of H SO on the solution and let it soak in.

D.

i. Add 1 mol Zn to solution and stir occasionally. ii. Now add a few mL of HCl (it removes the zinc). iii. Set up a vacuum filtration system and slowly pour your solution in it iv. Once product is obtained (pure copper), transfer to weighing paper and tare its

mass.

Data Analysis: From the results (obtaining pure copper through the cycle), it can be concluded that our proposed series of reactions was correct. Of course, metallic copper was our beginning reactant. Then HNO was added, followed by NaOH, and H SO . A negligible amount of zinc was added and then removed by a negligible amount of HCl. The ending product was pure copper. Here is the experiment series layed out by chemical reactions:

(a) Cu(s) + 4HNO (aq)

Cu(NO ) (aq) + 2NO (l) + 2H O (l)

(b) Cu(NO ) (aq) + 2NaOH(aq) (c) Cu(OH) (s) + H SO (aq) (d) CuSO (aq) + Zn(s)

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

precipitate forms

CuSO (aq) + 2H O(l)

ZnSO (s) + Cu(s)

pure copper is left

Conclusion: There were a couple of unusual findings in this experiment. When the copper was mixed with HNO there was a very vigorous reaction, which we did not expect. We also thought that it wouldn't happen as quickly as it did. Also, we were surprised to see that only twenty seconds in the centrifuge could separate the supernatant/precipitate as well as it did. It seems that solution usually

need longer in a centrifuge to produce the same result. This experiment showed that copper can be taken through a series of reactions with other chemicals to produce copper as a final product. This is why is it called a "copper cycle", because copper is the beginning element and the final product.