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Chemistry of Copper

Chemical change occurs whenever chemical bonds are broken and/or new chemical bonds areformed. During the chemical reaction, one or more substances are produced. Chemical reactions can be

classified in several ways. In this experiment, you will be exploring the different types of chemical

reactions.

Copper is a metal belonging to group IB in the periodic table. It is relatively inert and does not

readily oxidize in air. It reacts with concentrated nitric acid forming Cu2+ ion. You will observe several

chemical properties of copper through a series of reactions shown below:

Safety

Concentrated nitric acid is very corrosive both to the skin and to the eyes. In addition, sodium

hydroxide, sulfuric acid and hydrochloric acid are also corrosive. Wash with water immediately if any

of these compounds comes into contact with the skin. If you spill any on yourself or on the table,

immediately flood the area with water and call your instructor. Wear goggles at all times during this

experiment.

Procedure

A. Reaction of Copper Metal

Weigh approximately 0.02-g sample of Cu metal and place in a 4-in. test tube. Perform this

next step in the fume hood because of the evolution of a toxic gas. Add concentrated HNO 3 dropwise

( 10 drops) to the copper sample until no further evidence of chemical reaction is observed. DO NOT

ADD AN EXCESS! (Caution: Nitric acid stains the skin!)

At this point the Cu metal has completely reacted. Take note of the color of the solution.

(Caution: Do not inhale the evolved gas.) What is the color of the gas? Add 10 drops of distilled water.

Be sure to write down all your observations. Show the resulting solution to your instructor for approval

and save the solution for Part B.

B. Preparation of Copper (II) Hydroxide

Shake the test tube while slowly adding 10 drops of 6M NaOH. (Caution: Do not let NaOH

touch the skin!) Record any change in color of the solution and describe the precipitate. Add 10 more

drops of 6 M NaOH. Centrifuge the solution for 30 seconds.

Chemistry of Copper 1

Cu

Cu(NO3)

2CuSO

4

Cu(OH)2

CuO

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Test for complete precipitation by adding 2-3 more drops of 6M NaOH to the supernatant. If

additional precipitate forms, add 4-5 more drops of NaOH and centrifuge. Repeat the test until no

further formation of Cu(OH)2 occurs. The solution should appear colorless. Decant and discard the

supernatant from the test tube. Wash precipitate with 1 mL distilled water. Centrifuge again. Decant and

discard the wash water. Obtain your instructors approval before proceeding to part C.

C. Conversion of Copper (II) Hydroxide to Copper (II) Oxide

Slowly heat the test tube containing the precipitate from part B. The precipitate should change

color. You need not heat the contents to dryness. Avoid projection of your copper compound by not

holding the test tube over the direct flame for a prolonged period of time. Obtain your instructors

approval before proceeding to Part D.

D. Dissolution of Copper(II) Oxide

To the precipitate in the test tube from Part C, add 6M H2SO4 dropwise ( 20 drops). Shake

the test tube until the precipitate dissolves. (Caution: Do not let sulfuric acid touch the skin!) Take note

of the color of the resulting solution. Obtain your instructors approval before proceeding to part E.

E. Reduction of Cu(II) ions to metallic copper.

To the solution from Part D, gradually add with shaking zinc dust in minute amounts.

(Caution: Shake until no further reaction is observed before adding more zinc to make the solution

colorless. Record your observations.

Test for the completeness of the reaction by adding a few drops of the solution into a test tube

containing 1 mL 6M NH3. If a colored solution is obtained, add more zinc into the solution with

shaking. Repeat the process until a colorless solution is obtained.

Decant and discard the supernate. Wash the precipitate twice using 2-mL portions of water.

Decant and discard the wash water after each washing. Transfer the precipitate in a small beaker. Add

10 mL water and 2 mL 6M HCl slowly and stir the contents until no more change is observed.

(Caution: Do not let hydrochloric acid touch the skin!) Record your observations. Dispose of your

solution into the waste jar.

Data and Results

Part Observations Instructors Approval

A

B

C

D

E

Write the pertinent chemical equations for each part.

Modern Experiments for General Chemistry2

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Discussion

Discuss the chemical reactions that take place in this experiment. Classify the reactions

according to type.

Questions

1. What is the gas that is evolved in Part A?

2. When the NaOH solution is added, Cu(OH)2 does not precipitate immediately. What are

the other components of the reaction mixture from Part A that reacts with NaOH before the

copper ion? Explain.

3. Why must HCl be added to the solid after the reaction with zinc dust is completed?

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?

5. What volume, in drops, of concentrated HNO3 is required to react with 0.0191 g of Cu

metal? Assume 20 drops per milliliter.

Reference:

Beran, J.A.,Laboratory Manual for Principles of General Chemistry, NJ: John Wiley & Sons, c. 2000.

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