Where does the Water of UPS battery go?

Picture by ignatius.edu

A common question in our everyday life is "Where does the Water of UPS battery go?"

In order to understand this vanishing of water, we take a look at the composition UPS(Lead Storage Battery).

UPS battery contains an anode made up of lead, cathode made up of lead dioxide and an electrolyte which is Sulfuric acid.

When discharging takes place, lead anode is oxidized while at cathode reduction takes place.

(+) electrode (Cathode): PbO₂(s) + 4H⁺(aq) + SO₄^2-(aq) + 2e^- → PbSO₄(s) + 2H₂O(l)

(-) electrode (Anode): Pb(s) + SO₄^2-(aq) → PbSO₄(s) + 2e^-

There are two reasons for water disappearance:

1. Heat is produced during the reactions which vaporizes water.

2. H+ ions and OH- ions from water may get discharged at the electrodes as they have strong tendency to get discharged and hence they may contribute towards water loss.

3. During discharging water is converted into hydrogen and oxygen as the electrode reactions are reversible.