Barium peroxide

Barium peroxide is an inorganic compound with the formula BaO2. This white solid (gray when impure) is one of the most common inorganic peroxides, and it was the first peroxide compound discovered. Being an oxidizer and giving a vivid green colour upon ignition (as do all barium compounds), it finds some use in fireworks; historically, it was also used as a precursor for hydrogen peroxide.

Structure
Barium peroxide consists of barium cations Ba(2+) and peroxide anions O2(2-). The solid is isomorphous to calcium carbide, CaC2.

Preparation and use
Barium peroxide arises by the reversible reaction of O2 with barium oxide. The peroxide forms around 500 °C and oxygen is released above 820 °C.
 * 2 BaO + O2 ⇌ 2 BaO2

This reaction is the basis for the now-obsolete Brin process for separating oxygen from the atmosphere. Other oxides, e.g. Na2O and SrO, behave similarly.

In another obsolete application, barium peroxide was once used to produce hydrogen peroxide via its reaction with sulfuric acid:
 * BaO2 + H2SO4 → H2O2 + BaSO4

The insoluble barium sulfate is filtered from the mixture.