Microscale displacement of silver

EQUIPMENT:

• Copper wire

• 0.1 M silver nitrate solution

• Cavity slide

METHOD:

Search ‘Camera’

• Pipette

• Microscope (x40 objective)

• Clear sticky tape

1. Tape the wire across the cavity of the slide.

2. Place the slide under on the microscope stage and focus in until you get a clear image on the x40 objective.

3. Add 1 or 2 drops of silver nitrate solution to the cavity.

4. Watch the reaction occur (may be slow to start).

THE SCIENCE BIT…

This demonstration can be interpreted in different ways depending on the curriculum point and age of the students:

√ The reactivity series of metals:

Most Reactive Least Reactive

In its simplest interpretation, since copper is more reactive than silver it will displace silver in the reaction: Silver nitrate + copper → copper nitrate + silver

Thus silver crystals will form in the solution, and can be observed ‘growing’ under the microscope.

Other scientific interpretations:

√ Metallic structure and bonding of metals, using silver crystal formation as an example of metallic structure.

√ Simple electrochemical circuit:

Silver (Ag+) ions pull electrons off the silver crystals, which in turn remove electrons from the lump of copper (Cu) which produces Cu2+ ions, thus setting up a simple electrochemical circuit. For each copper ion that forms in solution, two silver ions will add to the silver crystal structure.

The ionic half equations are: Ag+ + 2e- → 2Ag and: Cu→ Cu2+ + 2e-