When to use a 12% oxidizing lotion

Oxidizing acids - a special form of acids

According to the Brönstedt definition, acids are chemical substances that can give off a proton, i.e. substances that have at least one hydrogen atom. In addition to these classic acids, there are also acids that not only release protons, but are also able to oxidize other substances. These acids, which act as oxidizing agents (especially their acid residues), are also known as “oxidizing acids”.


Oxidizing acids

With the subject of “oxidizing acids” many have difficulties in everyday school life, this is because the term “oxidizing acids” is technically ambiguous. When an acid such as hydrochloric acid (which is not defined as an oxidizing acid) reacts with a metal such as magnesium, the metal salt is formed (the metal is oxidized) and hydrogen (the protons of the acid are reduced). Therefore every metal is “actually” oxidized by an acid, so that every acid is an “oxidizing acid”. The reason why acids are classified as “normal” acids (e.g. hydrochloric acid) and oxidizing acids (e.g. nitric acid) is due to the fact that a distinction is made between base metals and so-called semi-precious metals.

Both oxidizing and non-oxidizing acids act as proton donors. They give off one (or more) protons to a reaction partner. The proton as an oxidized form can enter into a “redox reaction” with suitable metals (base metals) according to the electrochemical series, whereby the metal is oxidized and the proton is reduced to hydrogen. This is possible with both types of acid.

In the case of an oxidizing acid, however, one does not mean that the reactant is oxidized by the proton, but rather by the acid residue. This would be difficult to imagine with hydrochloric acid, for example. The chloride ion (the acid residue) is already reduced (has 8 valence electrons), so this ion has no tendency to withdraw electrons from another substance (and thus to oxidize this substance).

An oxidizing acid therefore not only has a proton that can oxidize base metals, but also an acid residue that, due to its position in the electrochemical series, can also oxidize noble metals (e.g. gold). This can be proven, for example, by allowing copper to react with hydrochloric acid and nitric acid. Due to its potential (approx. 0.35 V), copper is a noble metal and can therefore not be oxidized by a proton (0.00 V). Therefore, hydrochloric acid does not react with copper either. Nitric acid, on the other hand, reacts with copper, producing a “brownish” mist. A detection of hydrogen fails. In the case of hydrochloric acid and nitric acid, the proton did not react with the metal. In the case of nitric acid, however, the acid residue has reacted with the metal:

4 ENT3 + Cu -> Cu (NO3)2 + 2 NO2 + 2 H.2O

A distinction is therefore made between oxidizing and non-oxidizing acids. Non-oxidizing acids (such as hydrochloric acid, phosphoric acid, but also dilute nitric acid) only react as acids, i.e. they give off their proton, which can react with a suitable reaction partner (electrochemical potential <0.00 V). Therefore, non-oxidizing acids only react with base metals. In the case of oxidizing acids (such as nitric acid or hot concentrated sulfuric acid), the acid residue can also oxidize a reaction partner.

Why an oxidizing acid or part of it acted as an oxidizing agent has already been indicated. So that the “acid residue” of an oxidizing acid can (still) oxidize another substance, this part of the acid must be reducible. The chloride ion has already reached the lowest oxidation level (oxidation level -I), which is why the chloride ion no longer oxidizes other substances. In contrast, the nitrogen atom in nitric acid, for example, has an oxidation state of + V, so the NO3- to NO2 be reduced. Therefore every acid residue (which has one or more strongly electronegative elements in its structure - usually oxygen acids) can have a central atom with a high positive oxidation state. These central atoms or central atom groups can thus oxidize other substances.