Hydrogen- the most abundant element in the universe! -Part 12-

Concentration of hydrogen ions (H+) and acidity:

Corrosive symbol- Pixabay

Definitions of an acid and a base are pertinent in this context. The Swedish scientist Arrhenius provided the first generally accepted definition of an acid in 1887, defining it as a substance that releases hydrogen ions (H+) when it comes into contact with water, in contrast to a base, which releases hydroxide ions (OH-):
HCl=== H+ + Cl-
NaOH=== OH- + Na+
Because it doesn't account for all solvents and connects the problem of acidity to water, this theory has become insufficient. In addition, it was found that hydrogen ions are not found in water in this form (H+), but rather bond with the water molecule (H20) in the form of hydronium (H3O+).

As part of their theory that the acid-base reaction involves proton transfer and that the base is a proton acceptor and the acid a proton donor, Bronstedt and Lowry first proposed a more general definition of acids and bases in 1923. The benefit of this theory is that it demonstrates the close connection between the acid and the base and that it can identify the acid and base regardless of the solution in which the reaction process occurs.

• It's a general definition. Whether the substances are in solution or not doesn't affect its validity. The kind of the solution has no bearing on it (aqueous or non-aqueous).

The proton is given off by HCl acid in the water:
HCl + H2O === H3O+ + Cl-
And because it was the one who accepted the proton in the previous reaction, water acts as a base. Similar to how ammonia gas reacts with HCl gas, the first is regarded as basic and the second as acidic:
HCl(g) + NH3(g) === NH4Cl

• This theory also makes it possible to define the acid's strength. Strong bases take more protons and bind to them tightly, while strong acids are those that release more protons. As a result, HCl behaves as a strong acid in water because it almost completely ionizes, providing protons to the water. However, the acidic substance at this point is H3O+ ions, not HCl. Due to the complete protons donation they make to any base they come into contact with, H3O+ are a potent acid. In general, we note that new acid and base are created (a conjugate acid and a conjugate base) when an acid and a base react.

Lewis also noted that some neutralization reactions, like the reaction of NH3 with BF3, do not involve the transfer of any protons, which provides a more broad definition of acidity and basicity. Lewis therefore defined an acid as any substance that accepts a pair of electrons, with the base acting as the pair's donor.

Bibliographic references:

• [General and inorganic chemistry book- M. Shkhashirou- H. Birqdad- Y. Qodsi- University publications. Algeria]

• Hydrogen- Wikipedia

• Atome d'hydrogène- Wikipedia

• Acids, bases, pH, and buffers- Khan academy

• [Smail Meziane: Livre Chimie générale- Structure de la matiére. Berti edition, Alger, 2006]

• [Livre- Chimie génerale- R.Ouahes]