Catalysis of the reaction between zinc and sulfuric acid

This is a quick and easy experiment that can be done individually or in pairs.

Equipment

Apparatus

• Eye protection
• Test tubes x3
• Test tube rack
• Measuring cylinder, 10 cm³
• Dropping pipette

Chemicals

• Granulated zinc, a few pieces
• Copper turnings or powder, a few pieces / half a spatula
• Dilute sulfuric acid, 1 M (IRRITANT), 15 cm³
• Copper(II) sulfate(VI) solution, 0.5 M, a few cm³

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection.
• Dilute sulfuric acid, H₂SO₄(aq) (IRRITANT) – see CLEAPSS Hazcard HC098a, CLEAPSS Recipe Book RB098 and CLEAPSS L195 ‘Safer chemicals, safer reactions’.
• Copper(II) sulfate(VI) solution, CuSO₄(aq) – see CLEAPSS Hazcard HC027c and CLEAPSS Recipe Book RB031. 

Procedure

1. Put a few pieces of granulated zinc into each of the three test tubes. Try to have approximately the same amount in each test tube.
2. Add 5 cm³ of dilute sulfuric acid to test tube 1. Note the rate of production of gas bubbles.
3. Add a few copper turnings to test tube 2. Make sure they are in contact with the zinc. Add 5 cm³ of dilute sulfuric acid and note the rate of production of gas bubbles.
4. Add 5 cm³ of dilute sulfuric acid to test tube 3. Then add about 1 cm³ of the copper sulfate solution using a dropping pipette. Note the rate of production of gas bubbles. Note what happens to the colour of the copper sulfate solution. Note what happens to the surface of the pieces of zinc.

Teaching notes

If the granulated zinc pieces are shiny then the reaction in test tube 1 is slow. The reaction may be faster if the zinc is not very pure. Bubbles of hydrogen form on the surface of the zinc. The reaction is:

Zinc + Sulfuric acid → Zinc sulfate + Hydrogen
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

In test tube 2, copper is the catalyst for the reaction, and the reaction should be faster than in test tube 1, but may not be as fast as test tube 3.

In test tube 3, zinc displaces copper from the copper sulfate solution and the surface of the zinc goes black. The displaced copper metal then acts as a catalyst for the reaction.

Zinc + Copper sulfate → Zinc sulfate + Copper
Zn(s) + CuSO₄ (aq) → ZnSO₄(aq) + Cu(s)

There may be enough hydrogen produced in test tube 3 for students to test for using a lighted splint.