Chemical Reactions II: Oxidation/Reduction
5.6 Reduction of Cu2+ by Aluminum
Subjects: Oxidation/Reduction, Net ionic equations
Description: When a ball of aluminum foil is placed in a copper solution with chloride ions, the copper ions are reduced to copper metal and a coating of copper is seen on the surface of the aluminum.
- 400 mL beaker
- 1 M Copper sulfate‡
- 1 M Sodium chloride‡
- Ball of aluminum foil
- Stir rod
- Digital stand-alone thermometer
- Optional: Vernier Thermometer and Go-Link interface. Thermometer and interface require Logger Lite or Logger Pro software to display temperature.*
‡Solutions are located in the solutions cabinets.
*Vernier sensors and interfaces are located in the drawers oppisite the bin storage shelves.
- Add the solutions to the beaker and stir.
- Place the foil ball into the solution.
- Observe the copper metal forming on the aluminum.
- Measure the temperature rise of the solution.
The unbalanced net ionic equation for the reaction is given below:
Al(s) + Cu2+(aq) → Al3+(aq) + Cu(s)
1. Aluminum is oxidized. The oxidation state increases from zero to plus three (3 electrons lost). The copper is reduced. The oxidation state decreases from 2+ to zero (2 electrons gained). The two half-reactions are as follows:
Cu2+(aq) → Cu(s) (reduction) Al(s) → Al3+(aq) (oxidation)
2. The reactions are already balanced for mass. 3. To balance the half reactions for charge add the appropriate number for electrons:
2e- + Cu2+(aq) → Cu(s) (reduction) Al(s) → Al3+(aq) + 3e- (oxidation)
4. Multiply by an appropriate factor:
3[2e- + Cu2+(aq) → Cu(s)] (reduction) 2[Al(s) → Al3+(aq) + 3e-] (oxidation)
5. Add the half reactions to get the net ionic equation:
3Cu2+(aq) + 2Al(s) → Cu(s) + 2Al3+(aq)
This reaction is exothermic and the temperature rise of the solution can be measured using a thermometer.
Disposal: Dispose of solutions in appropriate aqueous waste containers.
1. J. Kotz, P. Treichel, J. Townsend. Chemistry & Chemical Reactivity. 7th Ed. Teachers Ed; Brooks/Cole; 2009; p. 900. Figure 20.2. Example 20.1
Note: All foil has a coating of aluminum oxide (Al2O3) that protects it from further reacting. The chloride ions in the solution breach the coating, allowing the reaction to take place.