Exothermic Zinc and Copper Sulfate Reaction

Zinc is added to aqueous copper sulfate in an insulated cup and the temperature rise of the solution is measured. The maximum temperature is used to determine the temperature change and estimate the heat released by the displacement reaction.

1. Prepare a simple calorimeter by placing a clean polystyrene cup inside a 250 mL beaker for stability and add a loose-fitting lid with a hole for a thermometer or temperature probe.
2. Measure 50.0 mL of copper sulfate solution of known concentration into the cup and record its initial temperature after allowing the probe to equilibrate.
3. Weigh an excess portion of zinc (for example 1.5 to 2.0 g of clean zinc granules or powder) on weighing paper so it can be added quickly in one portion.
4. Start a timer, remove the lid, add the zinc to the solution in one portion, immediately replace the lid, and insert the probe through the hole.
5. Stir gently but continuously with the probe or a plastic stirrer so heat is distributed evenly without splashing.
6. Record the temperature every 10 to 15 seconds until it reaches a clear maximum and begins to fall; note the highest reading as the peak temperature.
7. Calculate the temperature change ΔT as peak temperature minus initial temperature.
8. Estimate the enthalpy using q = mcΔT
9. Filter or decant to separate any unreacted zinc if needed and place liquids and solids in a labeled waste container for appropriate disposal.

Experiment: Temperature Changes in a Displacement Reaction - KEGS Chemistry:

Investigating Temp Changes Copper Sulfate and Zinc - Philip Russell:

• Use a temperature probe with data logging and plot temperature versus time to read an extrapolated peak.
• Compare different initial concentrations of copper sulfate to see how ΔT changes.
• Compare zinc granules versus zinc powder to observe differences due to surface area.
• Prewarm or prechill the copper sulfate solution to explore the effect of starting temperature on the measured peak.

• Copper sulfate solution is harmful if swallowed and irritating to eyes and skin; avoid contact and wash spills with plenty of water.
• Zinc powder can be an inhalation hazard; handle gently to avoid dust. Use granules where possible.
• The reaction is exothermic; the cup and contents may get hot enough to be uncomfortable. Keep the vessel on the bench and do not seal it tightly.
• Do not dispose of copper-containing solutions down the drain.

• Why does the temperature increase during this reaction? (Chemical potential energy is released as heat when zinc displaces copper from solution, making the process exothermic.)
• What assumptions are made when using q = m c ΔT in this setup? (That the solution has the same specific heat capacity and density as water, heat loss to surroundings is small, and the calorimeter heat capacity is negligible.)
• Why use a polystyrene cup instead of glass? (It reduces heat loss because polystyrene is a better thermal insulator.)
• Why add zinc in excess? (To ensure copper sulfate is the limiting reagent so the extent of reaction is well defined.)
• How could you reduce experimental error in ΔT? (Use a lid, minimize delays when adding zinc, stir consistently, use a data logger and extrapolate back to the mixing time.)