Question

When hydrogen peroxide antiseptic is tightly capped and left on the shelf for a long period of time, the bottle is observed to swell. When opened, it “hisses” noticeably. Explain these observations. Is the antiseptic likely to be as effective?

Answer 1

Answer:

The hydrogen peroxide decomposes as: $H_2O_2\rightarrow 2H_2O+O_2$

Explanation:

Hydrogen peroxide antiseptic although tightly capped but left on the shelf for a long time leads to swollen bottle and opens with a hissing sound because hydrogen peroxide reacts with air in presence of light to dissociate into water and oxygen molecules that leads to high volume of content in the tightly closed bottle and formation of water molecules from hydrogen peroxide.

Once the hydrogen peroxide has turned into water molecules it is no longer effective as an antiseptic.