The #K_a# of carbonic acid is #4.3 xx 10^-7# #H_2CO_3 rightleftharpoons H^+ + HCO_3^-#. What does this mean for #H_2CO_3#?

Question

The #K_a# of carbonic acid is #4.3 xx 10^-7# #H_2CO_3 rightleftharpoons H^+ + HCO_3^-#.  What does this mean for #H_2CO_3#?

Caleb Adams · Accepted Answer

It means that carbonic acid is a weak acid.

The acid dissociation constant, #K_a#, is a measure of the extent to which an acid ionizes in aqueous solution. More specifically, the smaller the value of #K_a#, the lower the extent of the ionization. In other words, the lower the value of #K_a#, the more molecules of acid will not ionize, i.e. they will not donate a proton. In your situation, you are aware that the subsequent equilibrium #"H"_ 2"CO"_ (3(aq)) rightleftharpoons "H"_ ((aq))^(+) + "HCO"_ (3(aq))^(-)# possesses #K_a = (["H"^(+)] * ["HCO"_3^(-)])/(["H"_2"CO"_3]) = 4.3 * 10^(-7)# Since carbonic acid does not entirely ionize in aqueous solution, the very small value you have for the acid dissociation constant indicates that the equilibrium lies to the left. This suggests that carbonic acid is a weak acid. To put it another way, the reason carbonic acid is referred to as a weak acid is because, in comparison to its initial concentration, a solution of carbonic acid will not contain appreciable concentrations of hydrogen ions (and, implicitly, of bicarbonate ions). It is important to note that carbonic acid exhibits high instability in aqueous solutions, leading to the following equilibrium. #"CO"_ (2(aq)) + "H"_ 2"O"_ ((l)) rightleftharpoons "H"_ 2"CO"_ (3(aq))# a more precise explanation of the situation in solution. Thus, you could say that you've #"CO"_ (2(aq)) + "H"_ 2"O"_ ((l)) rightleftharpoons "H"_ 2"CO"_ (3(aq)) rightleftharpoons "H"_ ((aq))^(+) + "HCO"_ (3(aq))^(-)#

Natalie Anton · Answer

undefined The given Ka value indicates the acid dissociation constant for carbonic acid (H2CO3). It represents the equilibrium constant for the reaction of carbonic acid dissociating into a hydrogen ion (H+) and bicarbonate ion (HCO3-). A higher Ka value indicates a stronger acid, while a lower value suggests a weaker acid. In this case, carbonic acid is a weak acid because its Ka value is relatively small.

Xavier Avery · Answer

undefined The $K_a$ value of carbonic acid ($H_2CO_3$) indicates its acid dissociation constant. Specifically, it represents the equilibrium constant for the dissociation reaction of carbonic acid into a hydrogen ion ($H^+$) and bicarbonate ion ($HCO_3^-$). The value of $K_a$ indicates the extent to which carbonic acid dissociates into its ions in a solution. In this case, the value $4.3 \times 10^{-7}$ signifies that carbonic acid is a weak acid, as it only partially dissociates into $H^+$ and $HCO_3^-$ ions in solution.