Displacement reactions of metals on a microscale

In this experiment, students observe what happens when they add drops of copper(II) sulfate solution, magnesium nitrate solution, zinc chloride solution and iron(III) nitrate solution to copper, magnesium, zinc and iron metals. They then interpret their results to determine the order of reactivity of the metals, and write equations for the reactions they observed.

The practical should take approximately 20 minutes.

Equipment

Apparatus

• Eye protection
• Student worksheet
• Clear plastic sheet (eg ohp sheet)
• Magnifying glass

Chemicals

• Copper(II) sulfate, 0.2 mol dm^–3
• Iron(III) nitrate, 0.2 mol dm^–3
• Magnesium nitrate, 0.2 mol dm^–3
• Zinc chloride, 0.2 mol dm^–3
• Magnesium ribbon
• Zinc metal, small granules
• Iron filings or small nails
• Copper turnings

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection throughout (splash-resistant goggles to BS EN166 3).
• Copper(II) sulfate solution, CuSO₄(aq), 0.2 mol dm^–3 – see CLEAPSS Hazcard HC027c and CLEAPSS Recipe Book RB031. Copper(II) sulfate solution causes eye damage and is TOXIC to aquatic life.
• Magnesium ribbon – see CLEAPSS Hazcard HC059A. Magnesium ribbon is FLAMMABLE and gives off highly flammable gases in contact with acids.
• Zinc powder, Zn(s) – see CLEAPSS Hazcard HC107. Zinc powder is FLAMMABLE and hazardous to the aquatic environment.
• The following chemicals and substances are of low hazard:
  • Zinc chloride 0.2 mol dm^–3 – see CLEAPSS Hazcard HC108a.
  • Iron(III) nitrate, Fe(NO₃)₃.9H₂O(aq), 0.2 mol dm^–3 – see CLEAPSS Hazcard HC055C and CLEAPSS Recipe Book RB052.
  • Magnesium nitrate, MgNO₃.6H₂O(aq), 0.2 mol dm^–3 – see CLEAPSS Hazcard HC059b.
  • Iron filings or small nails – see CLEAPSS Hazcard HC055A.
  • Copper turnings – see CLEAPSS Hazcard HC026.

Procedure

1. Cover the table on your worksheet with a clear plastic sheet.
2. Place a copper turning in each box in the copper row.
3. Place one small piece of magnesium ribbon in each box in the magnesium row.
4. Place a few zinc granules in each box in the zinc row.
5. Place an iron nail in each box in the iron row.

When all the pieces of metal are in place:

6. Add two drops of copper(II) sulfate solution to each metal in the first column. Observe and record your observations.
7. Add two drops of magnesium nitrate solution to each metal in the second column. Observe and record your observations.
8. Add two drops of zinc chloride solution to each metal in the third column. Observe and record your observations.
9. Finally, add two drops of iron(III) nitrate solution to each metal in the fourth column. Observe and record your observations.

Questions for students

1. What is the order of reactivity of the metals?
2. Write equations for any reactions that you observe.

Expected observations

The zinc granules and magnesium ribbon rapidly darken in copper sulfate solution as they become covered with a layer of copper. Iron also reacts but the change is not so clear. Magnesium and zinc react with the iron(III) nitrate, the solution gradually darkens.

No reaction occurs between magnesium sulfate and any of the metals. Students should observe no change between any of the metals and a salt solution of the same metal.