Aimee Lorraine C. Capinpuyan Locker # 7CExperiment No. 5 – Chemistry of Copper Aug. 16, 2010

Abstract The objectives of this experiment were to recover the 0.2 g Cu from the beginning of the

experiment, and to classify the types of chemical reactions that took place. By reacting copper with several chemicals, we were able to observe the various chemical changes that the copper underwent. These were characterized by changes in color and the formation of precipitate, to name a few. The resulting equations were balanced and classified as either precipitation reaction, acid-base reaction, or redox reaction.

IntroductionThere three major classes of chemical reactions are precipitation reactions, acid-base

reactions, and oxidation-reduction or redox reactions. Precipitation reactions are characterized by the formation of precipitate or solid particles. Acid-base reactions occur when an acid reacts with a base to form a salt and water. The acid, as defined in Principles of General Chemistry, acts as an H+ donor, while the base becomes an OH- donor. Finally, in a redox reaction, atoms appear as free elements on one side of the chemical equation, and as part of a compound on the other. In this experiment, we will try to classify each reaction of copper as one of these three types.

MethodWe start out with approximately 0.2 g Cu, a bronze-colored metal. In reaction A, we add

ten drops or less of nitric acid (HNO3) to produce a green liquid, copper (II) nitrate [Cu(NO3)2] and a yellowish hydrogen gas. Next, for reaction B, we add ten drops of sodium hydroxide (NaOH) to form the blue precipitate, copper (II) hydroxide [Cu(OH)2], and sodium nitrate (NaNO3). For reaction C, we heat the copper (II) hydroxide to release the water molecules from the solution, leaving only copper (II) oxide, CuO. In reaction D, we add sulfuric acid (H2SO4) to produce a light blue liquid, which is a mixture of copper (II) sulfate (CuSO4) and water. For the last reaction, reaction E, we add zinc, which bonds with SO4 to isolate copper.

ResultsTable 1 - Description of Reactions

R* Equation Observations

A Cu(s) + HNO3(aq) Cu(NO3)2(aq) + NO2(aq) + H2O(l)Green liquid and yellowish gas were

formed, solution grew warmer

B Cu(NO3)2 (aq) + NaOH (aq) Cu(OH)2 (s) + NaNO3 (aq)

Blue, gel-like precipitate was formed, along with visible brown and green particles.

Solution became hotter.

C Cu(OH)2 (s) CuO (s) + H2O (l)

Precipitate turned black. Bubbles formed at the bottom while heating.

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D CuO (s) + H2SO4 (aq) CuSO4 (aq) + H2O (l)Precipitate dissolved into hot, light blue

liquid.

E CuSO4 (aq) + Zn(s) Cu(s) + ZnSO4 (aq)

Solution became extremely hot. Brown solid was formed. The solution remained

light blue.*R = Reaction

Calculations Balancing the equations:

A. Cu(s) + 4HNO3(aq) Cu(NO3)2(aq) + 2NO2(aq) + 2H2O(l)

B. Cu(NO3)2 (aq) + 2NaOH (aq) Cu(OH)2 (s) + 2NaNO3 (aq)

The rest of the equations are already balanced.

DiscussionI. Classification of reactions

A. Reaction A was a redox reaction, since Cu appeared as an element on the left side of the equation and then became part of a compound [copper (II) nitrate] on the other. Specifically, it is a single displacement redox reaction, because Cu displaced H in HNO3.

B. Reaction B was a precipitation reaction, because of the formation of solid particles of copper (II) hydroxide.

C. Reaction C was a redox decomposition reaction, because copper (II) hydroxide “decomposed,” or broke down, into separate compounds.

D. Reaction D is a redox reaction, more specifically, a double displacement reaction, because Cu displaced H, and SO4 displaced O.

E. Reaction E is also a redox reaction, but this time, it is single displacement, since Zn displaced Cu.

II. Answers to Questions

1. What is the gas that is evolved in Part A? The NO2 would be the gas that is evolved.

2. What are the other components of the reaction mixture from part A that reacts with NaOH before the copper ion? Explain.

The sodium hydroxide first reacts with the excess nitric acid. The sodium hydroxide neutralizes the nitric acid, and then reacts with copper (II) nitrate. The chemical equation of the neutralization would be:

HNO3, HNO3(aq) + NaOH(aq) NaNO3(aq) + H2O(l)

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3. Why must HCl be added to the solid after the reaction with zinc dust is completed? This was done to cleanse the copper of any remaining particles of zinc.

4. A 0.0217 g sample copper metal is recycled through the series of reactions in this experiment. In part E, 0.0183 g sample of copper is isolated. What is the percent recovery of the copper metal?

Percent recovery = mass of recovered coppermass of original copper

= 0.0183 g Cu0.0217 gCu

= 0.843 x 100 = 84.3%

5. What volume, in drops, of concentrated HNO3 is required to react with 0.0191 g of Cu metal? Assume 20 drops per milliliter.

0191 g Cu x 1mol Cu

63.55 g Cux

4 mol HNO 31 molCu

x1 L HNO 3

16 mol HNO 3x

1mL HNO 30.001 L HNO 3

x20 drops HNO 3

1mL HNO 3=0.1.5 drops HNO3

ConclusionIn conclusion, copper underwent a series of chemical reactions of varied types before it

was recovered. These reactions are displacement (redox) for part A, precipitation for part B, decomposition (redox) for part C, double-displacement (redox) for part D, and finally, single-displacement (redox) for part E.

References

- http://www.scribd.com/doc/22269144/Copper-Reactions- http://www4.cord.edu/chemistry/krogstad/Chem127/127Lab/Exp4.pdf- Principles of General Chemistry, M. Silberberg

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