ChemTalk

Acid Naming Rules

acetic acid

Core Concepts

In this article, you will learn the basic definitions of what makes up an acid, as well as the acid naming rules. You will also learn about how strong and weak acids disassociate in water.

Topics Covered in Other Articles

What is an Acid?

An acid is a molecule or ion capable of donating a proton, known as a Brønsted–Lowry acid. An acid can also be defined as a molecule forming a covalent bond with an electron pair, known as a Lewis acid. Acids are always going to be ions or molecules. How is an acid a molecule? Well, all acids are made up of non-metals and a molecule is just another name for a covalent bond. Hydrogen ions (also known as protons because hydrogen only contains one proton), are a key element in what an acid is. Another good way to identify acids is to look for the (aq) symbol in chemical equations. This indicates the solution is aqueous, meaning it will be dissolved in water. If one of the species that will be aqueous is H+, then that is indication of an acid.

Most of us have heard of acids before, but what classifies an acid as strong or weak? Whether the hydrogen atom completely disassociates or only partially disassociates determines if the acid is strong or weak. This means that for a strong acid when the acid is placed in a beaker of water the hydrogen ion will be found 100% detached from its original molecule in solution. There are only six strong acids: sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, and perchloric acid.

Let us use HCl (hydrochloric acid) and HF (hydrofluoric acid) as examples.

Chemical formula for hydrochloric acid: HCl(aq)→ H+(aq)+ Cl–(aq)

HCL in H2O example of a strong acid for acid naming rules conventions
The HCl completely disassociates in the beaker because it is a strong acid.

Chemical formula for hydrofluoric acid: HF(aq)⇄ H+(aq)+ F–(aq)

HF in H2O example for acids
There are still intact HF molecules in the beaker because HF is not a strong acid.

Based on the chemical equations HCl completely disassociates because it is a strong acid. However, the HF has equilibrium arrows in its equation because there will be intact HF in solution as well as just the fluoride and hydrogen ion. The HF will attach to a water molecule and form hydronium which will make the solution basic.

How to Name Acids

Naming Acids with Oxygen

Example number one nitric acid-

  • First – Identify the polyatomic anion HNO3→ NO3– realize that this is nitrate
  • Second – Write the name of the polyatomic ion NO3– = Nitrate
  • Third – Change the suffix -ate into -ic Nitrate → Nitric
  • Fourth – Add the word acid to the name (Nitric Acid)

Example number two sulfurous acid-

  • First – Identify the polyatomic anion HSO3→ SO3-2 realize that this is sulfite
  • Second – Write the name of the polyatomic ion SO3-2 = Sulfite
  • Third – Change the suffix -ite into -ous Sulfite → Sulfurous
  • Fourth – Add the word acid to the name (Sulfurous Acid)

(The spelling of phosphate also changes to phosphoric acid to sound better)

It is a good idea to memorize the list of common polyatomic ions because the acids that contain oxygen have those polyatomic anions in them.

Common Polyatomic Ions that are need in acid naming rules
List of common polyatomic ions (some may be more common than others)

To summarize the acid naming rules for acids with oxygen – polyatomic anions ending in -ate become is -ic acids. Polyatomic anions ending in -ite become the -ous acids

Writing the Chemical Formulas for Acids with Oxygen

Example number one Chloric Acid-

  • First – write the symbol for the hydrogen cation – H+ = hydrogen ion
  • Second – Identify the polyatomic anion in the name of the acid by replacing the suffix -ic with the suffix -ate Chloric Acid → Chlorate
  • Third – write the chemical formula for the polyatomic anion Chlorate = ClO3–
  • Fourth – Combine the chemical formula for the hydrogen cation and the polyatomic anion H+ and ClO3– have a 1:1 ratio 1(+1) + 1(-1) = 0 . This means the compounds are neutral HClO3
  • Fifth – Write the subscript (aq) so we know the substance is an aqueous solution.

Naming Acids without Oxygen

Example number one HCl –

  • First – Identify the monatomic anion HCl → Cl–
  • Second – Write the name of the monatomic anion Cl– = Chloride
  • Third – Replace the suffix -ide in the monatomic anion with -ic. Chloride → Chloric
  • Fourth – Add the prefix Hydro and the word Acid. Thus, you get Hydrochloric Acid

Example number two H2S –

  • First – Identify the monatomic anion H2S → S-2
  • Second – Write the name of the monatomic anion S-2 = Sulfide
  • Third – Replace the suffix -ide in the monatomic anion with -ic. Sulfide → Sulfuric (the spelling is changed a bit to make it sound better).
  • Fourth – Add the prefix Hydro and the word Acid. Thus, you get Hydrosulfuric Acid

(The spelling of phosphorus also changes to phosphoric)

To summarize the acid naming rules for acids without oxygen – The chemical name of acids that do not contain oxygen always begins with the prefix -hydro and ends with the suffix -ic.