Permanganic acid

Permanganic acid is an unstable, strong, oxidizing acid with a formula of HMnO₄

Properties

Physical

Anhydrous permanganic acid does not exist. Solutions of permanganic acid (up to 20%) are purple liquids. The crystallohydrate (HMnO₄*2H₂O) is a purple crystalline solid that decomposes above 20 degrees Celsius.

Chemical

It is a very strong oxidizer, though milder than its anhydride, manganese heptoxide. It spontaneously decomposes, evolving oxygen and precipitating manganese dioxide, which catalyzes further decomposition of the acid.

By cooling the unstable concentrated solution of the acid near the freezing point, the crystallohydrate can be prepared. Sources vary about the nature of this compound: according to some sources, it is a hydronium salt of permanganic acid, according to others, it is a complex polymanganic acid.

Preparation

Permanganic acid can be prepared by dissolving manganese heptoxide in water, or by reacting barium permanganate with sulfuric acid.

Handling

Safety

Not much is known about the hazards of permanganic acid, but one should treat it with respect, as it is both a strong acid and a strong oxidizer.

Storage

It is impractical to store this acid because of its instability.

Disposal

Permanganic acid can be dumped in the ground, because it causes the compound to decompose, oxidizing the soil and turning into the safe, insoluble manganese dioxide. But it is better to dispose it after it is already decomposed in the lab.