Oxyacids and polyprotic acids


Definition of an oxacid
Acids are compounds that can donate H+ ions in water solutions.
Ternary acids also known as OXOACIDS or oxyacids contain three elements, H , O and a central atom, like HNO3. These types of acids usually have hydrogen attached to oxygen. The hydrogens are on the "edge" of the moleculare structure. The oxygen is conected to a central atom. Examples of common ternary acids are:
HNO3, HNO2, H2SO4, H2 SO3, H3PO4, H3PO3, H2CO3
You should see a common characteristic in these acids. They all have a nonmetal element as a central atom. They all have oxygens that are bridges between the hydrogen and the central atom. These substances are acids because the connection or bond between H and O is weak in these compounds. The H-O bond breaks with the formation of a H+ ion and a polyatomic anion.



nitric acid



nitrate ion


+ H2O


H1+ (aq)

+ NO31- (aq)

HNO3+ H2O ---> H1+ (aq) + NO31- (aq)

The (aq) means the ion is dissolved in water. The ion is in an aqueous mixture.


The oxy acids or ternary acids have their origins in oxides of the nonmetals like CO2(gas). The strange thing about this is that these nonmetal oxides form acids when they mix with water. These compounds are the villains that cause the acid rain problem.


carbon dioxide


carbonic acid


+ H2O

---> H2CO3 (aq)

The (aq) means the particle is dissolved in water. The particle is in an aqueous mixture.


Polyprotic acids
Acids with more than one acidic proton/hydrogen can release all of the protons. Thedescription of these acids ilinked to the multiple number of acidic hydrogen atoms. A diprotoic acid has "two" acidic hydrogens. A triprotic acid has "three" acidic hydrogens. This means H2SO4 has two acidic hydrogens that can be released form each formula unit.

sulfuric acid


two protons

sulfate ion





2 H+ (aq)




The (aq) means the particle is dissolved in water. The particle is in an aqueous mixture.

A triprotic acid is phosphoric acid, H3PO4
Non-acidic hydrogens
These ideas explain why hydrocarbon compounds like gasoline and butane, C4H10, are not acids even though there are many hydrogen atoms in the molecule. In hydrocarbons, hydrogen atoms are attached to carbon. The C-H bond is nonpolar and strong. Hydrocarbons are not acidic because H is not bonded to an atom in Group 6A or 7A.
A key idea is that an acidic hydrogen atom must be bonded to one of these atoms
F, Cl, Br, I, O or S


 Online Introductory Chemistry

Dr. Walt Volland, all rights reserved 1997-2005 revised May 1, 2005