Modern storage cells (batteries) can be divided into the non-rechargeable kind (primary cells) and the rechargeable kind (secondary cells).
Primary cells include the zinc / carbon / manganese oxide cell (check out the video below).
Secondary cells include the lithium ion cell and lead-acid batteries.
- Zinc / carbon cell
- Long-life alkaline battery
Practice question
In a lead acid battery the electrolyte is sulphuric acid, one electrode is lead and the other is lead(IV) oxide. When the battery is producing a voltage, both electrodes are converted to solid lead(II) sulfate.
Suggest half equations for the reactions happening in the battery.
Answer
At the lead electrode:
Pb(s) + SO42-(aq) ⇾ PbSO4(s) + 2e– or Pb(s) + H2SO4(aq) ⇾ PbSO4(s) + 2H+(aq) + 2e–
At the lead(IV) oxide electrode:
PbO2(s) + SO42-(aq) + 4H+(aq) + 2e– ⇾ PbSO4(s) + 2H2O(l)
Exam tip: think logically – in both half equations the product is lead sulfate, and we must have an oxidation and reduction half equation.
You could start by writing a half equation for Pb ⇾ Pb2+ + 2e– and then work from there for the oxidation half equation.
We know the electrolyte is sulfuric acid so there are plenty of H+ for the reduction half equation.
By-products are always common molecules and ions such as H+, O2-, OH–, H2O etc.