A strong acid is a completely dissociated or ionized acid in an aqueous solution . It is a chemical species with high capacity to lose a proton, H +. In water, a strong acid loses a proton, which is captured by water to form the hydronium ion:
HA (aq) + H 2 O ? H 3 O + (aq) + A – (aq)
Diprotic and polyprotic acids may lose more than one proton, but the “strong acid” pKa value and the reaction only refers to the loss of the first proton.
Strong acids have a small logarithmic constant (pKa) and a large acid dissociation constant (Ka).
Most strong acids are corrosive, but some of the super acids are not corrosive. On the contrary, some of the weak acids (for example, hydrofluoric acid) can be highly corrosive.
As the concentration of acid increases, the ability to dissociate decreases . Under normal conditions in water, strong acids dissociate completely, but extremely concentrated solutions do not.
Examples of strong acids
While there are many weak acids, there are few strong acids. Common strong acids include:
- HCl (hydrochloric acid)
- H 2 SO 4 (sulfuric acid)
- HNO 3 (nitric acid)
- HBr (hydrobromic acid)
- HClO 4 (perchloric acid)
- HI (hydrochloric acid)
- p-toluenesulfonic acid (organically soluble strong acid)
- methanesulfonic acid (a strong organic liquid acid)
The following acids dissociate almost completely in water , so they are often considered strong acids, although they are no more acidic than the hydronium ion, H3O +.
- HNO 3 (nitric acid)
- HClO 3 (chloric acid)
Some chemists consider that hydronium ion , bromic acid, periodic acid, perbromic acid and periodic acid are strong acids.
If the ability to donate protons is used as the main criterion for acid strength, then strong acids (from strongest to weakest) would be:
- H [SbF 6 ] (fluoroantimonic acid)
- FSO 3 HSbF 5 (magic acid)
- H (CHB 11 Cl 11 ) (superacid carborane)
- FSO 3 H (fluorosulfuric acid)
- CF 3 SO 3 H (triflic acid)
These are the ” superacids “, which are defined as acids more acidic than 100% sulfuric acid.
Examples of strong acid ionization reactions
HCl ? H + + Cl –
HNO 3 ? H + + NO 3 –
H 2 SO 4 ? 2H + + SO 4 2-
The production of positively charged hydrogen ions and the reaction arrow, which only points to the right, must be taken into account. The reagent (acid) is ionized in the product.
Factors that determine the strength of the acid
You may be wondering why strong acids dissociate so well, or why certain weak acids do not completely ionize. Some factors come into play:
- Atomic radio. As the atomic radius increases, so does the acidity. For example, HI is a stronger acid than HCl (iodine is an atom larger than chlorine).
- Electronegativity The more negative electronics a conjugate base is in the same period of the periodic table (A-), the more acidic it will be.
- Electric charge The more positive the charge on an atom, the greater its acidity. In other words, it is easier to take a proton from a neutral species than from a negatively charged one.
- Balance. When an acid dissociates, equilibrium is reached with its conjugate base. In the case of strong acids, the balance strongly favors the product or is to the right of a chemical equation. The conjugate base of a strong acid is much weaker than water as the base.
- Solvent In most applications, strong acids are evaluated in relation to water as a solvent. However, acidity and basicity have a non-aqueous solvent value. For example, in liquid ammonia, acetic acid is completely ionized and can be considered a strong acid, although it is a weak acid in water.