Single Displacement Reaction: Zinc and Copper(II) Ion REDOX

When zinc metal is immersed in a solution of 0.1 M aqueous copper(II) sulfate solution copper metal plates out on the zinc. The solution is initially blue in color. A dark coating of copper metal appears on the zinc within two minutes and when 45 minutes have elapsed, there is a thick coat of copper metal powder on the zinc strip and the blue color of the solution has lightened considerably.

Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s)

Zinc atoms are oxidized to Zn2+(aq):  Zn(s) -> Zn2+(aq) + 2e-    (loss of electrons)

Copper(II) ions are reduced to Cu(s):  Cu2+(aq) 2e-> Cu(s)     (gain of electrons)

This demonstration should also include having students predict whether or not copper will react with ZnSO4(aq).

 Cu(s) + Zn2+(aq) -> No reaction

Zinc is a more active metal compare to copper.  The Zn2+(aq) ions do not serve as a reducing agent.

Curriculum Notes 

This is a great demo to present at the beginning of a unit on electrochemistry because it can be followed later in the unit by the zinc/copper cell demo. This demo can also be used when discussing single-replacement reactions, redox reactions, or electronegativity. 

Active Learning

Please consider not lecturing to your students.  Use a series of well crafted questions, visualizations and a POGIL-ish tutorial to guide your students to understanding under what conditions single displacement reactions will occur.

The effectiveness of the demonstration is increased when 1) students are led through a guided-inquiry instructional sequence, 2) students view a computer animation representing what occurs at the atom level: the oxidation of zinc and the reduction of Cu2+ ions, and 3) students work the activity sheet that accompanies the demonstration and computer simulation.  A set Power Point slides attempting to infuse some active learning in the presentation of this demonstration is posted on the menu to the right.

Activity Series of Metals Computer Simulation

Select various metals to test in aqueous M2+ solutions.  Build an activity series of meals based upon observations of whether or not a metal reacts with a M2+aqueous solution.  Option to view a computer animation at the particle level of the interaction of the M2+ion with the metal electrode.  Based on observations, write the the oxidation-reduction half-reactions.

http://pages.uoregon.edu/tgreenbo/redox2.html

http://intro.chem.okstate.edu/1515F01/Laboratory/ActivityofMetals/home.html

©2010 Greenbowe  Chemistry Education Instructional Resources.

This is an OLD  FLASH-based computer simulation developed by Tom Greenbowe and his chemistry education research group.  A new HTML5 based computer simulation of this activity is planned to be developed.

Purdue University's chemistry demonstration web site  has an excellent "movie" of this lecture demonstration

http://chemed.chem.purdue.edu/demos/main_pages/9.11.html

Learning Objectives   

After viewing the demonstration and the computer animation at the particle level (molecular scenes), students should be able to

1.  write the oxidation half-reaction and the reduction half-reaction

2.  identify what is being oxidized and wht is being reduced

3.  explain why zinc is a more active metal when compared to copper

4. explain what causes the aqueous copper(II) sulfate solution to be blue and why the blue color fades as the reaction proceeds

Lead Time 
One day of lead time is required for this project.
Discussion 
  • Oxidation-reduction reactions involve the transfer of electrons between substances. In this reaction, zinc atoms each will lose two electrons (oxidation) and become Zn2+ ions.  The two electrons that are released by zinc will be gained by the Cu2+ ions (reduction). The Cu2+ ions become Cu atoms.

  • Total equation: Zn (s) + CuSO4 (aq) --> Cu (s) + ZnSO4 (aq)
    • Net ionic equation: Zn (s) + Cu2+(aq) --> Cu (s) + Zn2+(aq)
  • Since the copper(II) ion has substantially greater reduction potential (+0.15 V) than zinc ion (-0.76 V), it is readily reduced by zinc metal.

  • The blue color of the aqueous copper(II) sulfate solution is due to the presence of the hexaaquacopper(II) ion in water. The solution becomes lighter in color as copper(II) ions, Cu2+(aq). in the solution is replaced by zinc(II) ions, Zn2+(aq).
Materials 
  • 500 mL 0.1M CuSO4 solution
  • 2 ea. 400 mL beakers
  • glass stirring rod
  • 6.5 x 20 cm zinc strip
Procedure 
  • It is best to initiate this demo towards the beginning of the class period so that there is plenty of time for the reaction to proceed.
  • This demo should be projected for large classes.
  • To initiate the reaction, suspend the zinc strip by the glass rod so that it is immersed in the solution in one of the beakers.
  • After two minutes have elapsed, pull the strip out of the beaker and show the class how the portion that was in the solution has darkened.
  • Return to the demo several times during class to see how the reaction is proceeding.
  • By the end of class, the solution with the zinc strip in it should be considerably lighter in color.
  • Use the beaker with no zinc in it as a control. By comparing the reaction solution with the control, the students can see that the reaction solution has become lighter in color.
Safety Precautions 
  • Copper sulfate is moderately toxic. Handle with care.
  • Reserve the control solution for use the next time that demo is performed.
  • Dispose of wastes in accordance with Federal, state, and local regulations.
Footnotes 

References

1. Shakhashiri, Bassam Z.   Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 3, p. 122.

Prep. Notes 
  • Pour about 250 mL of copper sulfate solution into each of the beakers.
  • Fold the zinc strip in half over the glass rod.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group