List of the Strong Acids and Key Facts

In chemistry, there are seven "strong" acids. What makes them "strong" is the fact that they completely dissociate into their ions (H⁺ and an anion) when they are mixed with water. Every other acid is a weak acid. Because there are only seven common strong acids, it is easy to commit the list to memory.

List of the Strong Acids

Note that some chemistry instructors may refer only to six strong acids. That typically means the first six acids on this list:

1. HCl: Hydrochloric acid
2. HNO₃: Nitric acid
3. H₂SO₄: Sulfuric acid
4. HBr: Hydrobromic acid
5. HI: Hydroiodic acid (also known as hydriodic acid)
6. HClO₄: Perchloric acid
7. HClO₃: Chloric acid

Other Strong Acids

There are other strong acids, but they aren't encountered in everyday situations. Examples include triflic acid (H[CF₃SO₃]) and fluoroantimonic acid (H[SbF₆]).

Are Strong Acids Always Strong?

As the strong acids become more concentrated, they may be unable to fully dissociate. The rule of thumb is that a strong acid is 100 percent dissociated in solutions of 1.0 M or lower concentration.

Dissociation and pKa Values

The general form of the dissociation reaction of a strong acid is as follows:

HA + S ↔ SH⁺ + A^-

Here, S is a solvent molecule, such as water or dimethyl sulfoxide (DMSO).

For example, here is the dissociation of hydrochloric acid in water:

HCl(aq) → H⁺(aq) + Cl^-(aq)

A strong acid has a pKa value less than -2. The pKa value of the acid depends on the solvent. For example, hydrochloric acid has a pKa value of about -5.9 in water and -2.0 in DMSO, while hydrobromic acid has a pKa value around -8.8 in water and about -6.8 in DMSO.

A Closer Look at Some of the Strong Acids

• Hydrochloric acid: Hydrochloric acid also goes by the name of muriatic acid. The acid is colorless and has a pungent odor. Humans and most other animals secrete hydrochloric acid in the digestive system. The acid has many commercial applications. It is used to produce inorganic compounds, refine metals, pickle steel, and regulate pH. Of the common strong acids, it is one of the least hazardous to handle, least expensive, and easiest to store.
• Nitric acid: Nitric acid also goes by the name aqua fortis. It is a highly corrosive acid. While colorless in pure form, nitric acid yellows over time as it decomposes into nitrogen oxides and water. In chemistry, one of its key uses is for nitration. This is where a nitro group gets added to a molecule (usually organic). Nitric acids finds use as an oxidant in nylon production, as the oxidizer in rocket fuel, and as an analytical reagent.
• Sulfuric acid: Sulfuric acid (American spelling) or sulphuric acid (Commonwealth spelling) is also called oil of vitriol. It is colorless, odorless, and viscous. Pure sulfuric acid does not naturally exist because the acid so strongly attracts water vapor. It's a dangerous acid to handle because it is highly corrosive and powerfully dehydrates skin upon contact, causing both acid chemical burns and thermal burns. It's primary use is in the production of fertilizers. It is also used to make detergents, dyes, resins, insecticides, paper, explosives, acetate, batteries, and drugs. Sulfuric acid is also used in water treatment.

Sources

• Bell, R. P. (1973). The Proton in Chemistry (2nd ed.). Ithaca, NY: Cornell University Press.
• Guthrie, J.P. (1978). "Hydrolysis of esters of oxy acids: pKa values for strong acids". Can. J. Chem. 56 (17): 2342–2354. doi:10.1139/v78-385
• Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. ISBN 978-0-13-039913-7.
• Miessler G.L.; Tarr D.A. (1998). Inorganic Chemistry (2nd ed.). Prentice-Hall . ISBN 0-13-841891-8.
• Petrucci, R. H.; Harwood, R. S.; Herring, F. G. (2002). General Chemistry: Principles and Modern Applications (8th ed.). Prentice Hall. ISBN 0-13-014329-4.