Cu-Again!
!WORK IN PAIRS OR ALONE IF YOUR PARTNER IS ABSENT!
Introduction: Chemical reactions are often accompanied by formation of a precipitate, evolution of gas, change in color, or pronounced temperature
change. In this activity, you will observe these characteristics of chemical reactions. Enjoy the variety!
Purpose: To learn to recognize when a chemical reaction has occurred. To introduce names and formulas of chemicals. To see how atoms are neither
created or destroyed in a chemical reaction. To learn how to write chemical equations.
Safety Considerations: Wear protective glasses and an apron at all times. Avoid skin contact with solids and solutions. Dispose of all solutions in the
containers provided by your teacher. Wash your hands before leaving the laboratory.
Vocabulary Preview: Read the complete set of directions & underline the terms you don't understand. We will discuss these terms before beginning.
Recording the lab: We will record this experiment as a system of inputs and outputs for each chemical reaction in the series on the attached chart. For
each reaction record the following:
a) Before: Draw & label the original contents of the test tube.
b) Specify the INPUT required to make the contents transform in a chemical reaction.
c) After: Draw & label the reaction & your observations.
d) Record the names, formulas & (phases) of the products of each reaction.
Procedure: Check each step off as you complete & record the details in your observations chart on the following pages.
_____1. Your teacher will demonstrate for the class the REACTION 1 of metallic copper, Cu(s) with concentrated nitric acid, HNO3(aq). This must be done
in the fume hood. (Caution: Avoid breathing poisonous gases. Avoid contact of skin with nitric acid. It burns skin and clothing.) The products formed
are copper(II) nitrate solution, Cu(NO3)2(aq), water, H2O(l) and nitrogen dioxide gas, NO2(g).
_____2. Begin heating a beaker 2/3 full of water on a hot plate. One beaker per lab table is enough. If it begins to boil, turn the heat down.
_____3. A solution of copper(II) nitrate was prepared earlier. One of your thin-stem pipets contains this solution. Transfer all of the solution to your a
small test tube provided at your lab table.
_____4. Another thin stem pipet contains sodium hydroxide solution, NaOH(aq). (Caution: Avoid contact with sodium hydroxide; it burns skin.) Add
this slowly to the test tube. This REACTION 2 produces some heat. (In other words, it may be exothermic.)
_____5. Use a stir rod to mix the reactants thoroughly.
_____6. Add about 2 milliliters of distilled water. Tap or stir to mix. The solid material which makes the liquid opaque is copper(II) hydroxide,
Cu(OH)2(s). Aqueous sodium nitrate, NaNO3 is also present.
_____7. Place your test tube in the hot water bath you prepared earlier - use a test tube clamp from your drawer. Remove the test tube when you see no
further change occurring from REACTION 3. This product is copper(II) oxide, CuO(s) Water, H2O is a side product as well. Run cold water over the
outside of the test tube to cool it.
_____8. Allow the material to settle or use a centrifuge to spin down the solution. Decant or use the plastic pipet labeled "waste" to remove the clear
liquid (supernatant liquid) above the copper(II) oxide. Do not remove any of the solid.
_____9. Discard the liquid and wash precipitate by adding about 3 milliliters of distilled water. Tap or stir to mix.
_____10. Allow the solid to settle or use a centrifuge to spin the precipitate down. Then remove and discard the liquid, or centrifuge and decant.
_____11. To the precipitate, add hydrochloric acid, HCl(aq), from the final thin stem pipet. (Caution: Avoid contact of both skin and clothing with
hydrochloric acid.) Tap or stir to mix. This new product of REACTION 4 is copper(II) chloride solution, CuCl2(aq). Water, H2O is again a side product.
_____12. Your instructor will show you how to coil a piece of aluminum, Al, wire so that most of the wire is in the liquid while a hook on the allows you
to remove the wire when the reaction is completed. Place the test tube in a cold water bath (beaker). This reaction is very fast! (Be sure to use a test tube
holder since the reaction gives off considerable heat.) The products forming in REACTION 5 are hydrogen gas, H2(g), aluminum chloride solution,
AlCl3(aq), and metallic copper, Cu(s) and heat.
_____13. When the reaction has slowed down significantly, shake the copper off of the wire into the liquid. Spin down the solid in the centrifuge. Then
discard the waste liquid into the waste bucket.
_____14. Wash the remaining solid with about 3 ml of distilled water. Centrifuge & discard the liquid.
_____15. Show your test tube product to the instructor for checking before proceeding.
_____16. Take your product to the fume hood (or the courtyard behind A12). Test your product with a squirt of concentrated nitric acid. Record your
observations - REACTION 6 should look familiar. Leave the test tube in the fume hood.
_____17. Complete your notes. Determine the names and formulas of the products based on previous similar observations. Show the instructor your
notes.
_____18. Wash hands thoroughly before leaving the laboratory.
Analysis & Concept Development :
(12 pts) Use your observations to complete a drawing similar to the one below. Make the drawing large enough to fill a page so that it is easy to read.
Alongside each arrow: a) write in the chemicals used or input, b) write in key words to convey succinctly what you observed, c) draw arrows branching
off to indicate the formation of side products .
Writing Chemical Equations: Complete the chemical equations that occurred in the lab using formulas and symbols.
1) __Cu(s) + __ HNO3(aq) --> __ __________( ) + __ __________ ( ) + __ H2O(l)
2) __ Cu(NO3)2(aq) + __ NaOH(aq) --> __ __________( ) + __ _________( ) + heat
3) __ Cu(OH)2(s) + heat --> __ __________( ) + __ __________( )
4) __ CuO(s) + __ HCl(aq) --> __ __________( ) + __ __________( )
5a) __ CuCl2(aq) + __ Al(s) --> __ __________( ) + __ __________( )
5b) __ HCl(aq) + __ Al(s) --> __ __________( ) + __ __________( ) + heat
Conclusions (10 pts):
1. Why is this series of reactions called Cu-Again?
2. Where did each of the side products finally end up?
3. Which two reactions were exothermic? Which one was endothermic?
4. Define the following terms: physical change, chemical change, and ore.
5. What evidence of chemical change did you observe in the lab? Give 3 examples.
6. What is smelting? How is copper smelted from ore (find online)?
7. What common metals have you observed being recycled?
8. Why is recycling metals cheaper than producing new metal from mining?
9. How can techniques like these be used to obtain metals for use?
10. Propose questions related to the lab.
Cu-Again - Draw & label the experiment for each reaction & record your observations of color, matter & energy in the appropriate spaces.
Before
Input(s)
After
Output(s)