LAB: A Series of Copper Reactions

CHEMISTRY LAB
A SERIES OF COPPER REACTIONS

INTRODUCTION:

In this experiment you will take a copper sample through a series of five reactions. The end product will be your original copper sample, making this a cycle of reactions. With careful attention to quantitative lab practices, you should be able to recover all the copper you started with. Figure 1 is a diagram showing the order of the five reactions:

Each reaction has specific cautions to be observed. Pay close attention to the instructions. The following is the stoichiometry for each reaction:

(1) 8HNO_{3 (aq)} + 3Cu _(s) + O_{2 (g)} ----> 3Cu(NO₃)_{2 (aq)} + 4H₂O _(l) + 2NO_{2 (g)}

(2) Cu(NO₃)_{2 (aq)} + 2NaOH _(aq) ----> Cu(OH)_{2 (s)} + 2NaNO_{3 (aq)}

(3) Cu(OH)_{2 (s)} -- heat--> CuO _(s) + H₂O _(l)

(4) CuO _(s) + H₂SO_{4 (aq)} ----> CuSO_{4 (aq)} + H₂O _(l)

(5) CuSO_{4 (aq)} + Zn _(s) ----> ZnSO_{4 (aq)} + Cu _(s)

MATERIALS NEEDED:

Ring stand
Iron ring
Wire gauze
Bunsen burner
Infrared lamp (or other drying apparatus)
250-mL beaker
100-mL beaker
Porcelain evaporating dish
Spatula
Rubber policeman
Deionized water (both room temperature and hot)
Rinse bottle with deionized water

Chemicals

₃

₂

₄

If you need to build a substitute for the hood (figure 2)

SAFETY PRECAUTIONS:

SAFETY GOGGLES MUST BE WORN AT ALL TIMES

Reaction 1

Concentrated nitric acid, HNO₃, is hazardous. It causes severe burns to the skin, and the vapor is a lung irritant. Polyvinyl chloride gloves are suggested. Concentrated nitric acid should only be used in a fume hood. The dissolution of the copper wire with concentrated HNO₃ produces a brown gas, NO₂, which is very toxic and should be avoided. Figure 2 shows an apparatus that can be used in the absence of a fume hood.

Reaction 2

NaOH solutions are corrosive to the skin and especially dangerous to the eyes. Keep those safety goggles on !

Reaction 5

Methanol and acetone are flammable and their vapors are toxic. Use them in the hood to avoid breathing the vapors. Keep away from all open flames.

PROCEDURE:

1. Cut a length of pure copper wire that that has a mass of about 0.5 g. If it is tarnished, clean it with steel wool, rinse it with water, and dry it with a tissue or paper towel. Find the mass to the nearest 0.01 g and record the mass on the data table as mass of original copper sample. Coil the wire into a flat spiral, place it in the bottom of a 250-mL beaker, and in the fume hood, add 4.0 mL of concentrated (16M) nitric acid, HNO₃. Be sure to use the apparatus shown in figure 2 if a fume hood is not available. Record in the observations section a description of what you see. Swirl the solution carefully in the beaker until the copper has completely dissolved. Record in the observations section, what the solution is when the reaction is complete. After the copper dissolves, add deionized water until the beaker is about half full.

Steps 2 through 4 can be conducted at your lab station.

2. While stirring the solution with a glass rod, add 30 mL of 3.0M NaOH to precipitate Cu(OH)₂. Record your observations in the observations section. Also record what if formed in the solution besides Cu(OH)₂. Remember: rinse off the stirring rod back into the beaker with a small amount of deionized water from the rinse bottle, to keep from loosing any chemicals. You are being quantitative throughout this lab.

3. Set-up the apparatus as shown in Figure 3. Stirring gently with a glass rod to prevent bumping (caused by the formation of large steam bubbles formed in a locally overheated area), heat the solution just barely to the boiling point over a burner using the apparatus shown in Figure 3. If it bumps, you could loose some of the CuO, so keep stirring and turn the burner down when the boiling point is just reached, to maintain the temperature there. Record your observations in the observations section. When the reaction is complete, remove the burner, continue stirring for a minute or so, then allow the CuO to settle. Again, remember to rinse off the stirring rod, into the beaker, with a small amount of deionized water from the rinse bottle.

Now you are going to use the technique of decanting. Decanting is to pour off the supernatant liquid, being careful not to loose any of the precipitate, in this case CuO. This takes a steady hand. DonÕt try to pour off every bit of the liquid or you will loose some of the CuO. The rinses will take care of removing all the supernatant.

When the CuO has settled, carefully decant off the liquid, without loosing any CuO. Add about 200 mL of hot deionized water, allow to settle again, and decant once more. Answer the following question in the observations section. What is removed by the washing and decantation process?

4. Add 15 mL of 6.0M H₂SO₄, while stirring. In the observations section, record what you see, and what in in solution now.

Return to the fume hood

5. In the fume hood, add all at once 2.0 g of 30-mesh zinc metal, Stirring until the supernatant liquid is colorless. Record your observations, and what gas is produced, in the observations section. When the evolution of gas has become very slow, decant the supernatant liquid being careful not to loose any copper. If you can see any silvery grains of unreacted zinc, add 10 mL of 6M HCl and warm, but do not boil, the solution. When no hydrogen evolution can be detected by eye, decant the supernatant liquid and transfer the copper to a porcelain dish. Be sure to get all the copper, using a rubber policeman. Rinse the policeman with a small amount of deionized water over the dish. Wash the product with about 5 mL of deionized water, allow it to settle, and decant the wash water. Repeat the washing and decantation at least two more times. Wash with about 5 mL of methanol or acetone. allow to settle, and decant. Place the porcelain dish under an infrared lamp and dry the copper metal.

Find the mass of the 100-mL beaker to the nearest 0.01 g and record its mass in the data table. Using a spatula, transfer the dried copper metal to the 100-mL beaker and again find the mass to the nearest 0.01 g. Record this mass in the data table as mass of 100-mL beaker with copper sample.

DATA TABLE:

Mass of original copper sample. ________ g

Mass of empty 100-mL beaker. ________ g

Mass of 100-mL beaker with copper sample. ________ g

OBSERVATIONS:

From step 1

₃

______________________________________________________________________

What is the solution? ____________________________

From step 2

______________________________________________________________________

what if formed in the solution besides Cu(OH)₂? _____________________

From step 3

______________________________________________________________________

What is removed by the washing and decantation process?

____________________________

From step 4

₂

₄

______________________________________________________________________

What is in solution now?

____________________________

From step 5

______________________________________________________________________

What is the gas being produced? ________________

CALCULATIONS:

Calculate the mass of copper you recovered by subtracting the mass of the empty beaker from the mass of the beaker with the copper metal.

Mass of copper metal recovered. __________ g

Calculate the Percentage Recovery by the following formula:

Percentage recovery	=	mass of copper recovered mass of copper wire	x	100%

Percentage recovery. ______ %

If you were careful at every step you will have recovered nearly 100% of the copper you started with.

Back to Chemistry Table of Contents
Back to Lab Dad's Laboratory