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Naming Oxyacid and Oxoanions ( Covalent Acid )

Since we shall encounter few covalent ternary compounds that are not acid, only acids are discussed in this section. Examples of ternery acid include sulfuric acid, H2SO4 , Nitric Acid HNO3 and Boric Acid H3BO3.

Oxyacids are ternary acids that contain oxygen. Such compounds have hydrogens bonded to a oxyanion. For instance, if two hydrogens are attached tosulfate, SO42-, the resulting acid is called sulfuric acid. This name was obtained by adding ic acid to the end of the name of the non metal contained in sulfate.

Sulfuric acid = sulfur + ic Acid

Oxyanions that end in ate, when bonded to hydrogen(s), form oxyacids whose names are derived from the name of the nonmetal with ic acid as the ending.

If the nonmetal in the oxyacid exists in more than one oxidation state , then there is more than one oxyacid , each with a varying number of oxygen atoms, for example , consider two oxyacid containing H, O, and S :

H2SO4 = Sulfuric Acid

H2SO3 = Sulfurous acid

Sulfuric acid’s sulfur is in the +6 oxidation state, whereas , the sulfur in sulfuroius acid , H2SO3 is in the lower +4 state.

If two oxyacid exist with the same nonmetal , the acid containing the non metal in the higher oxidation state is given the ic acid ending ( corresponding to the oxyanion sulfate , SO42- ), ous acid is the ending for the oxyacid possessing the non metal in the lower oxidation state ( corresponding to the oxyanion sulfite, SO32- ).

Two oxyacid containing nitrogen exist; nitric acid , HNO3 , and nitrous acid HNO2 . nitric acid’s nitrogen is found in the +5 state, whereas nitrous acid’s nitrogen is in the +3 oxidation state.

HNO3 = Nitric Acid

HNO2 = Nitrous Acid

The names are derived from the oxyanions contained within the molecule . A nitrate , NO3- , is found in HNO3 accordingly ic acid is added to the stem nitr from nitrogen , giving nitric acid . A nitrite ion, NO2- is found in nitrous acid , thus , ous acid is added to the stem nitr , giving nitrous acid.

Oxyacid Oxyanion Name
Nitric Acid ( HNO3 ) No3- Nitrate
Carbonic Acid ( H2CO3) CO32- Carbonate
Sulfuric Acid ( H2SO4) SO42- Sulfate
Boric Acid ( H3BO3 ) BO33- Borate
Chloric Acid ( HClO3) ClO3- Chlorate
Selenic Acid ( H2SeO4 ) SeO42- Selenate

A few nonmetals from three or four oxyacids. Lets consider the four oxyacids of Cl :

HClO4, Perchloric Acid Cl = +7

HClO3 , Chloric Acid Cl = +5

HClO2 = Chlorous Acid Cl = +3

HClO = Hypochlorous Acid Cl = +1

Here, in addition to the acid with the ic and ous endings , two other acids exist , one with a Cl in higher oxidation state , and another in a lower state. When this situation arises, the acid containing the non metal in the highest oxidation state ( Contain one more O than the ic acid ) is named by placing per as a prefix , and attaching ic acid at the end. Similiarly, the acid with the nonmetal in the lowest oxidation state ( contain one less O than the ous acid ) is given a prefix of hypo with the ous acid ending.

When perchloric acid , HClO4 gives up a H+ , the ClO4- or Perchlorate ion result. Acids with per as the prefix and ic acid as an ending contain polyatomic ions that are named by dropping the ic acid and adding ate. Similiarly, acids with hypo and ous acid contain hypo… ite ion. Thus when HOCl loses a H+, a hypochlorite ion OCl-, result.

Example

Write the name for the following series of oxyacids, and the polyatomic ions contained within the molecules . (a) HBrO4, (b) HBrO3, (c) HBrO2 (d) HBrO

Answer :

a. HBrO4’s Br is found in the +7 oxidation state , the highest of the series , its named pebromic acid , and it contains the perbromate ion, BrO4-

b. HBrO3’s Br is found in the +5 state , and its named bromic acid , the BrO3- is the bromate ion.

c. HBrO2’s Br is in the oxidation state, and HBrO2 is called bromous acid; it contains a bromite ion, BrO2-

d. HBrO’s Br oxidation number +1 , and HBrO is hypobromous acid, BrO is the hypobromite

Unfortunately, there is no easy way of knowing which oxyacids exist for a particular nonmetal. It is a metter of sitting down and learning the most important ones, and referring to a table of oxyacids for the others. This table below gives a partial listing of additional common oxyacids.

Nonmetal Oxyacid Formula
P Phosphoric Acid
Phosphorous Acid
Hyphophosphorous Acid
H3PO4
H3PO3
H3PO2
Se Selenic Acid
Selenous Acid
H2SeO4
H2SeO3
B Boric Acid H3BO3
C Carbonic Acid H2CO3
Si Silicic Acid H4SiO4
As Arsenic Acid
Arsenous Acid
H3AsO4
H3AsO3

Acids containing more than one hydrogen ( H2SO4, H3PO4 … ) can lose some or all of their hydrogen ions in chemical reactions. If H2SO4 loses one H+, the resulting ion is HSO4- :

H2SO4 → H+ + HSO4-

HSO4- is named hydrogen sulfate . it is only necessary to affix the wor hydrogen to the name of the polyatomic ion , SO42-.

Phosporic acid, H3PO4 can give up one two, or three H+ ions . if one H+ is lost , then H2PO4-, dihydrogen phosphate , is produced. If two H+ ions are lost then HPO42-, monohydrogen phosphate results :

H3PO4 → H+ + H2PO4-
H3PO4 → 2H+ + HPO42-
H3PO4 → 3H+ + PO43-

Polyatomic ions containing hydrogen are named exactly the same way as other polyatomic ions. To name NaHCO3, it is only necessary to write sodium hydrogen carbonate. CaHPO4 is named Calcium monohydrogen phosphate.

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