Question #9f01e

1 Answer

Answer:

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.