How is acid/base chemistry defined and represented in aqueous solution?

Question

Henry Antrim · Accepted Answer

In water under standard conditions, we know that #K_a=[H_3O^+][HO^-]=10^-14#

(note that #H_3O^+# and #H^+# may be used equivalently. They represent the characteristic cation in water, #"the acidium ion."#)

We know (i) that #pH=-log_10[H_3O^+]#, and (ii) that under standard conditions of #1*atm# and #298*K#, #K_a=10^-14#. The basic concept of acid/base chemistry in aqueous solution is defined by (i) by definition and (ii) by VERY careful measurement. A solution is acidic if there there is a preponderance of the characteristic cation, #H_3O^+#. That is the solution is acidic if #[H_3O^+]>[HO^-]#, i.e. there are more so-called #"hydronium ions"# than #"hydroxide ions"# per unit volume. The solution is basic if #[H_3O^+]<[HO^-]#, i.e. there are LESS so-called #"hydronium ions"# than #"hydroxide ions"# per units volume. And if #[H_3O^+]=[HO^-]#, then the solution is NEUTRAL. #"For undergrads:"# we know that #K_a=[H_3O^+][HO^-]=10^-14# under standard conditions of #1*atm# (or whatever they use these days), and #298*K#. Under non-standard conditions, i.e. #T=373*K#, how do you think #K_a# would evolve?

Kai Bowman · Answer

undefined Acid/base chemistry in aqueous solution is defined and represented using the concepts of hydrogen ions (H⁺) and hydroxide ions (OH⁻). Acids are substances that release hydrogen ions when dissolved in water, while bases are substances that release hydroxide ions or accept hydrogen ions. The concentration of hydrogen ions determines the acidity of a solution, with lower pH values indicating higher acidity. Conversely, the concentration of hydroxide ions determines the alkalinity of a solution, with higher pH values indicating higher alkalinity. The reaction between an acid and a base in aqueous solution typically produces water and a salt.