Mineral Acids – Common Oxy Acid Terminology

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Mineral AcidsAs a youngster, I decided to become a chemist when I grew up. And that is how it turned out. To become acquainted with my chosen profession, I had to learn its naming systems or nomenclature. This included the naming of common mineral acids.

So called mineral acids contain hydrogen, at least one additional element (often from the right hand side of the periodic table), and varying amounts of oxygen.

Mineral Acids with No Oxygen

If no oxygen is present, the acid name usually employs the prefix hydro– and the suffix –ic. Thus HCl is named hydrochloric acid.¹ HBr is hydrobromic acid.

Some other examples include hydrogen sulfide (H₂S), hydrogen iodide (HI), and hydrogen telluride (H₂Te). A little confusion arises when the element has a valence greater than -2, as for phosphorous. Those substances usually are not considered acids.

One Atom of Oxygen

When hydrogen is united with the second element and is joined by a single atom of oxygen and the element has a -1 valence, the acid is given the prefix hypo– and the suffix –ous. Thus,

HClO is hypochlorous acid.
HBrO is hypobromous acid.

Two Atoms of Oxygen

Add another oxygen atom and the hypo– prefix disappears.

HClO₂ is chlorous acid.
HIO₂ is iodous acid.

Three Atoms of Oxygen

Add a third atom of oxygen and the –ous becomes –ic. This may confuse some, as it will be recalled the combination of hydrogen and chlorine with no oxygen is named hydrochloric acid! But note there is no hydro– prefix here. Thus,

HClO₃ is chloric acid.
HBrO₃ is bromic acid.

Four Atoms of Oxygen

Add one last oxygen atom. You get a peroxy acid. It has prefix per– and suffix –ic. This makes for an exceptionally powerful. It also makes for a powerful oxidizer

HClO₄ is perchloric acid.
HIO₄ is periodic acid.

There are alternative ways to name compounds. Still, it is essential to understand this system of nomenclature if one is to understand the chemical literature.

1 Actually, HCl is a gas, which is usually used dissolved in water. When it is the gas, HCl is called hydrogen chloride.

Note: You might also enjoy From Acids to Superacids: From Lavoisier to Olah


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