Question

Question #9f01e

Answer 1

Metallic salts like those of `"H"_2"O"_2` don't contain oxide ions. They contain peroxide ions.

Explanation:

The reason is partly historical and partly chemical.

If you follow the rules for naming covalent compounds, `"H"_2"O"_2` is dihydrogen dioxide.

Historically, the prefix "per-" usually means that a compound contains an extra oxygen atom. Recall that `"HClO"_3` is chloric acid and `"HClO"_4` is perchloric acid.

But the more important chemical reason is that metallic salts like sodium peroxide and barium peroxide don't contain oxide (`"O"^"2-"`) ions. They contain peroxide (`"O"_2^"2-"`) ions.

Compounds that are formed by combining an `"H"^+` ion with an anion can have two names.

Thus, pure `"HCl"` is hydrogen chloride, and the aqueous solution is hydrochloric acid.

Pure `"H"_2"SO"_4` used to be called hydrogen sulfate, but it is now almost always called sulfuric acid.

In the same way, `"H"_2"O"_2` was called hydrogen peroxide, and the name has stuck.