Oxyacids

   
 
What are they?  |  How are they named? If we know the formula  | If we know the name  |  Examples  |  IUPAC systematic nomenclatureExercises
   

What are they?

 They are called oxyacids, and have a general formula:

HaXbOc  

X is usually a nonmetal, but can be a transition metal in a high number oxidation, as Cr+6, Mn+6 or Mn+7.

How are they named?

    The IUPAC supports common nomenclature in this kind of compounds.

Common nomenclature.

    To formulate these compounds need to know the oxidation numbers of nonmetal X. They are as follows

Halogens +1, +3, +5, +7
Chalcogens +4, +6
Group of N +3, +5
Group of C +4

    In the acid formula deduce the oxidation number of element X (+ n) shall be equal to twice oxygens minus hydrogens. The result is divided by the number of atoms X.

    The oxidation number of X shown by some prefixes and suffixes.

Oxidation numbers Acid

Highest

High

Low

Lowest

per-      -ic

            -ic

            -ous

hypo-    -ous

    

If we know the formula

    In the formula: Deduce the oxidation number of the central element, as we saw it twice oxygens minus hydrogens, and as (highest, high, low or lowest) we termination appropriate (per-  -ic, -ic, ous- or hypo-  -ous). 

 

If we know the name

    In the name: Based on the prefixes and suffixes deduce the oxidation number of the central element. Hydrogen oxidation number +1  and oxygen -2. We look after coefficients so that the charge provided by the oxygens is equal and opposite to that provided by the hydrogens and the central element.

 

Examples

    The most common oxyacids are:

    HALOGENS: oxidation numbers: +1, +3, +5, +7.   Oxyacids form the Cl, Br, and I, but not the F.

 Oxidation Number (+1): HClO   hypochlorous acid
 ON (+3): HClO2   chlorous acid
 ON (+5): HClO3  chloric acid
 ON (+7): HClO4     perchloric acid

      CHALCOGENS: oxidation numbers: +4, +6.   Oxyacids of S, Se, Te.

 ON (+4): H2SO3     sulfurous acid
 ON (+6): H2SO4   sulfuric acid

    GROUP OF N: oxidation numbers: +3, +5. Oxyacids of N, P, As.

 ON (+3): HNO2  nitrous acid
 ON (+5): HNO3  nitric acid
 Also known N+1 :H2N2O2  diazenediol

   The oxyacids of P and As are 3 hydrogens.

 ON (+3): H3PO3   phosphorous acid
 ON (+5): H3PO4  phosphoric acid

    CARBON AND SILICON: oxidation number: +4.

 ON (+4): H2CO3  carbonic acid 
 ON (+4): (H2SiO3)n  metasilicic acid
 ON (+4): H4SiO4  silicic acid

    CHROMIUM AND MANGANESE: Also forming acids that transition metals, for example, Cr and Mn.

 ON (+6): H2CrO4  chromic acid
 ON (+6): H2Cr2O7  dichromic acid
 ON (+6): H2MnO4  manganic acid
 ON (+7): HMnO4  permanganic acid

 

IUPAC systematic nomenclature

      For oxyacids IUPAC proposed two nomenclatures, in addition to admit as valid common names, is the additive names and the hydrogen names.

      The additive names are based on the structure of the acid, naming differently the oxygen that are tied to the acid hydrogens (hydroxido), and the oxygen only united central element (oxido). These names carry prefixes corresponding di-, tri-, tetra- and so on. And are named in alphabetical order followed by the name of the central atom.

Prefix-hydroxido-prefix-oxido-CENTRAL ELEMENT

      The hydrogen names are formed by the word "hydrogen" with the prefix that shows us the number of atoms of hydrogen, between brackets the word "oxido" with the prefix that shows us the number of atoms of oxygen, followed by the central atom finished -ate.

Prefix-hydrogen(Prefix-oxido-CENTRAL ELEMENT-ate)

Formula Structural formula

Additive names

Hydrogen names

HClO Cl(OH)  hydroxidochlorine  hydrogen(oxidochlorate)
HClO2 ClO(OH)  hydroxidooxidochlorine  hydrogen(dioxidochlorate)
HClO3 ClO2(OH)  hydroxidodioxidochlorine  hydrogen(trioxidochlorate)
HClO4 ClO3(OH)  hydroxidotrioxidochlorine  hydrogen(tetraoxidochlorate)
H2SO3 SO(OH)2  dihydroxidooxidosulfur  dihydrogen(trioxidosulfate)
H2SO4 SO2(OH)2  dihydroxidodioxidosulfur  dihydrogen(tetraoxidosulfate)
HNO2 NO(OH)  hydroxidooxidonitrogen  hydrogen(dioxidonitrate)
HNO3 NO2(OH)  hydroxidodioxidonitrogen  hydrogen(trioxidonitrate)
H3PO3 P(OH)3  trihydroxidophosphorus  trihydrogen(trioxidophosphate)
H3PO4 PO(OH)3  trihydroxidooxidophosphorus  trihydrogen(tetraoxidophosphate)
H2CO3 CO(OH)2  dihydroxidooxidocarbon  dihydrogen(trioxidocarbonate)
H4SiO4 Si(OH)4  tetrahydroxidosilicon  tetrahydrogen(tetraoxidosilicate)
H2CrO4 CrO2(OH)2  dihydroxidodioxidochromium  dihydrogen(tetraoxidochromate)
H2Cr2O7 (HO)Cr(O)2OCr(O)2(OH)  μ-oxidobis(hydroxidodioxidochromium)  dihydrogen(heptaoxidodichromate)
H2MnO4 MnO2(OH)2  dihydroxidodioxidomanganese   dihydrogen(tetraoxidomanganate)
HMnO4 MnO3(OH)  hydroxidotrioxidomanganese  hydrogen(tetraoxidomanganate)

 

Exercises

In Formulae you have an exercise to write the names of these substances and to check your results. You also have the answer to the exercise.

In Names you have an exercise to write the formulae for these substances and to check your results. You have to introduce the formulae without subscripts, for example for water = H2O. You also have the answer to the exercise.

Formulae 1 Names 1 Formulae 2 Names 2 IUPAC Formulae 1 IUPAC Names1 IUPAC Formulae 2 IUPAC Names2

 
   

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