Slide presentation
Naming Oxoacids
General Chemistry • Chemical Compounds
Topic 1 · Acid naming
Naming Oxoacids
Oxoacids contain hydrogen, oxygen, and another central element. Their names come from the related oxyanion name.
Learning target
Connect oxyanion names to oxoacid names and write formulas from acid names using charge balance.
nitrate → nitric acid
Why it matters
Oxoacid names encode the parent oxyanion.
Names like nitric acid, sulfuric acid, and phosphoric acid are not random. They tell you which oxygen-containing ion becomes protonated by H+.
Laboratory acids
Nitric acid, sulfuric acid, and phosphoric acid are common reagents with names linked to nitrate, sulfate, and phosphate.
Formula writing
The oxyanion charge tells how many H atoms are needed in the acid formula.
Pattern recognition
The -ate and -ite endings help you predict acid names without memorizing every formula separately.
Core concept
Start from the oxyanion, then change the ending.
An oxoacid can be viewed as H+ combined with an oxygen-containing polyatomic ion. The acid name is built by changing the oxyanion ending.
1. Identify H
The formula begins with hydrogen because it is an acid.
2. Find oxygen
Oxoacids contain oxygen, unlike binary acids.
3. Identify oxyanion
Remove H+ mentally to reveal the related oxyanion.
4. Change ending
-ate becomes -ic acid; -ite becomes -ous acid.
Pattern: oxyanion name → oxoacid name. The central element stays the same, but the ending changes.
Vocabulary
Oxoacid naming depends on oxyanion endings.
The most important signal is whether the oxyanion ends in -ate or -ite. Prefixes such as per- and hypo- are usually kept.
| Oxyanion | Oxyanion name | Acid formula | Oxoacid name |
|---|---|---|---|
| NO3− | nitrate | HNO3 | nitric acid |
| NO2− | nitrite | HNO2 | nitrous acid |
| SO42− | sulfate | H2SO4 | sulfuric acid |
| SO32− | sulfite | H2SO3 | sulfurous acid |
| ClO4− | perchlorate | HClO4 | perchloric acid |
| ClO− | hypochlorite | HClO | hypochlorous acid |
Main rule
-ate becomes -ic acid, and -ite becomes -ous acid.
This rule connects the acid name to the oxyanion name. It is different from binary acid naming, which uses hydro-.
Examples: nitrate becomes nitric acid, while nitrite becomes nitrous acid.
Formula charge rule
An oxyanion with a 2− charge needs two H+ ions: sulfate, SO42−, becomes H2SO4.
No hydro- for oxoacids
HNO3 is nitric acid, not hydronitric acid, because it contains oxygen.
Interactive simulation
Choose an oxyanion and build its oxoacid.
The builder uses the oxyanion charge to add the correct number of H atoms, then converts the oxyanion name into the acid name.
Oxoacid name builder
Formula and name
HNO₃ — nitric acid
Nitrate ends in -ate, so the acid name ends in -ic acid.
Static fallback model
Nitrate is NO3−. Adding one H+ gives HNO3, named nitric acid.
The model shows naming pieces, not molecular geometry.
Dynamic relationship
The oxyanion family controls the acid family.
The visual compares related oxyanions and shows how their endings map to oxoacid names.
The canvas updates from the selected oxyanion in the builder.
Worked example
Name H2SO3.
The formula contains hydrogen, oxygen, and sulfur, so it is an oxoacid. Identify the related oxyanion after removing the H+ ions.
Recognize the acid type
H2SO3 contains H, S, and O, so it is an oxoacid.
Find the related oxyanion
Removing two H+ ions leaves SO32−, which is sulfite.
Apply the ending rule
Sulfite ends in -ite, so the acid ending becomes -ous acid.
Final answer: H2SO3 is sulfurous acid.
Common mistake
Do not add hydro- to oxoacid names.
The hydro- prefix belongs to binary acids such as HCl(aq). Oxoacids contain oxygen, so their names come from oxyanion endings instead.
Incorrect reasoning
“HNO3 starts with hydrogen, so it should be hydronitric acid.”
This ignores the oxygen-containing oxyanion nitrate.
Correct reasoning
NO3− is nitrate. Nitrate ends in -ate, so HNO3 is nitric acid.
Practice check
Name HClO2 and write the formula for phosphoric acid.
Question: What is the correct name of HClO2, and what formula represents phosphoric acid?
Show answer
Name HClO2
ClO2− is chlorite. Chlorite ends in -ite, so HClO2 is chlorous acid.
Write phosphoric acid
Phosphoric acid comes from phosphate, PO43−. Three H+ ions are needed, so the formula is H3PO4.
Reasonableness check
The acid formula must be neutral. A 3− oxyanion requires three hydrogen ions.
Apply the topic
Classify the acid before applying the naming rule.
If an acid contains hydrogen and one nonmetal with no oxygen, use binary acid rules. If it contains hydrogen, oxygen, and a central element, use oxoacid rules.
Open the calculator
Practice converting between oxyanion names, oxoacid names, and formulas.
Try related questions
Check your understanding of -ate, -ite, -ic acid, and -ous acid patterns.
Find H
Acid formulas usually begin with hydrogen.
Check for O
Oxygen means oxoacid rules apply.
Name oxyanion
Identify the related polyatomic ion.
Change ending
-ate → -ic, -ite → -ous.
Final summary
Oxoacid names are oxyanion names transformed into acid names.
Oxoacid formula
Contains hydrogen, oxygen, and another central element.
-ate rule
An -ate oxyanion becomes an -ic acid.
-ite rule
An -ite oxyanion becomes an -ous acid.
Formula writing
The oxyanion charge determines how many H atoms are needed.
Key idea: Do not memorize oxoacids one by one; connect each acid to its parent oxyanion.