Physical properties

Pure hydrogen peroxide is an almost colourless liquid, though it has a faint pale-blue tint in bulk. It is less volatile and more viscous than water.

Commercially, hydrogen peroxide solutions are labelled by their "volume strength" rather than by percentage concentration alone. A 30% solution of H₂O₂ is marketed as "100-volume" hydrogen peroxide, meaning that, at STP, 1 mL of this solution liberates 100 mL of oxygen gas on complete decomposition (heating). This volume-strength convention gives a quick practical ha …