Microscale reactions of metals with acids

In this microscale experiment, students observe the reactions of various metals with hydrochloric acid, nitric acid and sulfuric acid. They record their findings and attempt to explain them. Students may then be asked to write word and symbol equations for the reactions involved.

The practical should take about 20 minutes.

Equipment

Apparatus

• Eye protection
• Student worksheet
• Clear plastic sheet (eg ohp sheet)
• Magnifying glass
• Petri dish and lid

Chemicals

• Hydrochloric acid, 1 mol dm^–3
• Dilute nitric acid, 1 mol dm^–3
• Concentrated nitric acid, 5 mol dm^–3
• Sulfuric acid, 1 mol dm^–3
• Magnesium ribbon
• Zinc metal – small granules
• Iron filings
• Tin granules
• 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).
• Do NOT increase quantities mentioned and work in a well-ventilated laboratory. Nitrogen oxides are formed, gases are CORROSIVE and very TOXIC (fatal if inhaled) – see CLEAPSS Hazcard HC068B.
• Hydrochloric acid, HCl(aq), 1 mol dm^–3 is low hazard – see CLEAPSS Hazcard HC047a and CLEAPSS Recipe Book RB043.
• Dilute nitric acid, HNO₃(aq), 1 mol dm^–3 is CORROSIVE – see CLEAPSS Hazcard HC067 and CLEAPSS Recipe Book RB061.
• Concentrated nitric acid, HNO₃(aq), 5 mol dm^–3 is OXIDISING, CORROSIVE and gives off TOXIC fumes – see CLEAPSS Hazcard HC067 and CLEAPSS Recipe Book RB061.
• Sulfuric acid, H₂SO₄(aq), 1 mol dm^–3 is CORROSIVE – see CLEAPSS Hazcard HC098a and CLEAPSS Recipe Book RB098.
• Magnesium ribbon is FLAMMABLE – see CLEAPSS Hazcard HC059A.
• Zinc powder, Zn(s), is FLAMMABLE and hazardous to the aquatic environment – see CLEAPSS Hazcard HC107.

Procedure

1. Cover the table on your worksheet with a clear plastic sheet.
2. Place a few copper turnings 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 some iron filings in each box in the iron row.
6. Finally, place a few tin granules in each box in the tin row.

When all the pieces of metal are in place:

7. Add two drops of dilute hydrochloric acid to each metal in the hydrochloric acid column.
8. Add two drops of dilute nitric acid to each metal in the nitric acid column.
9. Add two drops of dilute sulfuric acid to each metal in the sulfuric acid column.
10. Finally, put one piece of copper turning into the Petri dish. Add two drops of concentrated nitric acid and immediately put on the lid.

Question for students

What did you observe? Give explanations for your observations.

Teaching notes and expected observations

The magnesium ribbon reacts vigorously with each acid. The zinc and iron also react, but less vigorously. In each case hydrogen gas is produced as well as the metal salt. The reaction between iron and nitric acid eventually produces a red-brown rust colour (iron(III) oxide). Students could link this with corrosion and acid rain. Tin and copper do not react with the hydrochloric and sulfuric acids but a few bubbles may be seen (using the magnifying glass) with the nitric acid.

The reaction between copper and concentrated nitric acid produces a blue solution and bubbles (of brown nitrogen dioxide). Students MUST put the lid over the Petri dish as soon as they add the acid. Nitrogen dioxide is very toxic.

Students can write word and symbol equations for the reactions involved.