An oxidizing acid is a
Brønsted acid that is a strong
oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ''electron donor''). In ot ...
. Most Brønsted acids can act as oxidizing agents, because the acidic proton can be reduced to
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
gas. Some acids contain other structures that act as stronger oxidizing agents than hydrogen ions. Generally, they contain oxygen in their anionic structure. These include
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
,
perchloric acid
Perchloric acid is a mineral acid with the formula H Cl O4. It is an oxoacid of chlorine. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxid ...
,
chloric acid
Chloric acid, H Cl O3, is an oxoacid of chlorine, and the formal precursor of chlorate salts. It is a strong acid ( p''K''a ≈ −2.7) and an oxidizing agent.
Properties
Chloric acid is thermodynamically unstable with respect to disproportio ...
,
chromic acid
Chromic acid is a chemical compound with the chemical formula . It is also a jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide.
The term "chromic ...
, and concentrated
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
, among others.
General properties
Oxidizing acids, being strong oxidizing agents, can often oxidize certain less reactive metals, in which the active oxidizing agent is not H
+ ions. For example,
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
is a rather unreactive metal, and has no reaction with concentrated
hydrochloric acid
Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
. However, even dilute nitric acid can oxidize copper to Cu
2+ ions, with the
nitrate
Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
ions acting as the effective oxidant:
: 3 Cu + 8 HNO
3 → 3 Cu
2+ + 2 NO + 4 H
2O + 6
Sometimes the concentration of the acid is a factor for it to be strongly oxidizing. Again, copper has no reaction with dilute
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
, but in concentrated sulfuric acid, the highly acidic environment and high concentration of
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
ions allow the sulfate ions to act as an oxidizing agent.
Sulfuric acid is not an oxidizing agent, but the sulfate ion is a very weak oxidizing agent. Since sulfur is in its maximum oxidation state in the sulfate ion, it cannot act as a reducing agent.
: Cu + 2 H
2SO
4 → SO
2 + 2 H
2O + + Cu
2+
See also
*
Reduction potential
Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
*
Standard electrode potential (data page)
The data below tabulates standard electrode potentials (''E''°), in volts relative to the standard hydrogen electrode (SHE), at:
* Temperature ;
* Effective concentration (activity) 1 mol/L for each aqueous or amalgamated (mercury-allo ...
References
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