Why are the Arrhenius definitions of acidity and alkalinity restricted to aqueous solutions?
Thanks for the excellent question on Arrhenius acids and bases.
According to Arrhenius, his definition of acids and bases arose from his study of electrolytes, which are almost always ions in solution. Thus, Arrhenius defined his acids as substances which produce hydrogen ions in aqueous solutions and bases are those substances which produce hydroxide ions in solution.
Since Arrhenius was the first scientist that we know of who tried to define the groups of chemicals known now as acids and bases, he could make up his own definitions based on his experimental data.
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