Acid Nomenclature

Core Concept

Naming acids follows a systematic set of rules based on the name of the anion (the negative ion) attached to the hydrogen cation ($H^+$). In aqueous solutions, these compounds release hydrogen ions, which is why their names are distinct from standard ionic compounds.

Binary Acids (-ide): Use the prefix hydro- and change the suffix to -ic (e.g., Chloride becomes Hydrochloric acid).
Oxyacids (-ate): Remove the prefix and change the suffix to -ic (e.g., Nitrate becomes Nitric acid).
Oxyacids (-ite): Remove the prefix and change the suffix to -ous (e.g., Nitrite becomes Nitrous acid).

Practice Tips

The "Hydro-" Clue: If you see the prefix hydro-, it is a signal that the acid is binary and contains only two elements (Hydrogen + one other).
Mnemonic for Oxyacids: Use the phrase "I ate something icky, and it was right ous for my appetite" to remember which anion suffix pairs with which acid suffix.
Identify the Ion First: Before naming, mentally remove the hydrogens and identify the polyatomic ion (e.g., in $HClO_4$, the ion is perchlorate, so the acid is perchloric acid).
Watch for Stem Changes: Be aware that for Sulfur and Phosphorus, the roots change slightly for better pronunciation (e.g., "sulf-" becomes "sulfur-" and "phosph-" becomes "phosphor-").

Test Yourself

Assorted Multiple Choice

Following the standard rules for naming binary acids, what is the correct name for a solution where gaseous hydrogen chloride is dissolved in water?

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Acid Nomenclature

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Acids that do NOT contain oxygen (Binary acids)

hydro______ic acid

The acid name comes from the root name of the anion name. The prefix hydro- and the suffix -ic are then added to the root name of the anion.

Examples:

HBr (aq) → hydrobromic acid
HI (aq) → hydroiodic acid
H₂S (aq) → hydrosulfuric acid

Acid that DO contain oxygen (Oxyacids):

______ic acid or _______ous acid or hypo ______ous acid

⚠️ You need to know your polyatomic ions well. See list here for reference.

Suffixes are used based on the ending of the original name of the oxyanion. If the name of the polyatomic anion ends with: -ate, change it to -ic for the acid

-ite, change it to -ous in the acid … if contains 1 fewer oxygen than “-ate” ion

-ite, change to hypo___ous acid … if contains 2 fewer oxygen than “-ate” ion

Examples:

H₂SO₄ (sulfate is SO₄²⁻) → sulfuric acid
H₂SO₃ (sulfite is SO₃²⁻) → sulfurous acid
HNO₃ (nitrate is NO₃⁻) → nitric acid
HNO₂ (nitrite is NO₂⁻) → nitrous acid
Note: Oxyacids do not use the “hydro-” prefix.

Brain Hack Tip

🧠 Here is a tip of how to remember how to remember how to name acids 🧠

My ride has hydrolics

Ends in “-ide” forms hydro __ic acid
Example: HBr … Br = Bromide, so hydrobromic acid.

I ate something icky

Ends in “-ate” forms __ic acid
Example: HNO3 … NO3- = nitrate, so nitric acid.

Sprite is delicious

Ends in “-ite” forms __ous acid
HNO2 … NO2- is nitrite, so nitrous acid.

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