Definition of an acid not dependent of the solvent?

Answer 1

The most general definition of an acid relies on Lewis acid/base theory, which defines an acid as a substance (usually an atom on a substance) that can accept an electron pair from another group.


For example, the proton H+ can accept a lone electron pair from OH- and is therefore an acid by the Lewis definition (it is also a Brønsted-Lowry acid as well). The hydrogens in the hydronium ion, H3O+ (a more accurate representation of the "lone" proton, which chemists often use only for convenience) are also Lewis acids by the same reasoning.


Iron(III) chloride, FeCl3, is an example of a Lewis acid that does not fit under the Arrhenius or Brønsted-Lowry definitions - it can accept a lone pair from, say, a chloride ion. This is particularly useful in Friedel-Crafts alkylation and acylation reactions.

Answer 2

An acid is a substance that donates protons (H+ ions) in a chemical reaction. It can be defined as a molecule or ion that can release hydrogen ions (H+) into a solution. This definition holds true regardless of the solvent in which the acid is dissolved.