Melt It, Split It

Why it matters

Solid lead bromide ignores the battery completely. Melt it, and the story flips: silvery beads sink at one rod while reddish-brown vapour curls off the other.

The idea in plain words

Balance check: PbBr₂ → Pb + Br₂. One lead, two bromines — nothing lost, just pulled apart by the current.

Predict first

Why must the lead bromide be molten before the battery can do anything?

Solid PbBr₂ already holds Pb²⁺ and Br⁻ ions — but locked in a lattice. Melting frees them to migrate, and only moving charges can carry current to the electrodes.

• Only in the melt are the ions free to move and carry the current — correct
• The heat itself decomposes the salt; the battery just watches
• Solid PbBr₂ contains no ions until it melts

What you do

Pass the current through the melt. Watch silvery lead collect at the cathode while reddish-brown bromine vapour rises off the anode.

Check yourself

What collects at the cathode (negative electrode)?

Pb²⁺ cations migrate to the negative cathode, gain electrons there, and settle as silvery molten lead.

Why is electrolysis of molten PbBr₂ a chemical (redox) change and not just melting?

Pb²⁺ is reduced at the cathode and Br⁻ is oxidised at the anode — two new substances appear. Electrolysis is redox driven by electric current.

The current is switched off mid-experiment. What happens at the electrodes?

Electrolysis is a forced, non-spontaneous change — the battery pushes it uphill. No current, no further reaction.

• Silvery molten lead — correct
• Reddish-brown bromine
• Hydrogen gas
• Ions gain or lose electrons at the electrodes, forming new substances — correct
• The salt simply melts and will re-freeze unchanged
• The bromine slowly dissolves the graphite electrodes
• The changes stop; the lead and bromine already formed stay as they are — correct
• The products recombine on their own into PbBr₂
• The reaction speeds up because the ions relax