Reaction of Zinc and Copper(II) Ion
Copper metal plates out on a strip of zinc metal when it is immersed in a solution of 0.1 M aqueous copper(II) sulfate solution. 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.
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. 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.
- 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.
- Total equation: Zn (s) + CuSO4 (aq) --> Cu (s) + ZnSO4 (aq)
- Net ionic equation: Zn (s) + Cu2+ (aq) --> Cu (s) + Zn2+ (aq)
- The blue color of the copper sulfate solution is due to the presence of the hexaaquacopper(II) ion. The solution becomes lighter in color as copper ion in the solution is replaced by zinc ion.
- 500 mL 0.1M CuSO4 solution
- 2 ea. 400 mL beakers
- glass stirring rod
- 6.5 x 20 cm zinc strip
- 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.
- 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.
- Pour about 250 mL of copper sulfate solution into each of the beakers.
- Fold the zinc strip in half over the glass rod.