Your answer to Practice Problem \(15.5\) shows the dissociation yielding 2 moles of protons per mole of acid, but this reaction actually produces fewer protons. Write the two balanced equilibrium equations for the dissociation of carbonic acid in water.

Diprotic acids are a type of acids that have two hydrogen ions (protons) that they can donate to a base during the acid-base reaction. Carbonic acid (\(H_2CO_3\)) is an example of a diprotic acid because it can lose two protons through sequential dissociation steps. The significance of being diprotic lies in the ability of the acid to undergo two levels of dissociation, each with unique equilibrium constants.

During the first step of dissociation, one hydrogen ion is released to form the bicarbonate ion (\(HCO_3^-\)), while the second dissociation step involves the release of another proton from the bicarbonate ion to form the carbonate ion (\(CO_3^{2-}\)). Understanding diprotic acids is vital in many chemical reactions, including metabolic processes and ocean chemistry.

The chemical equilibrium is the state of a reversible reaction where the rates of the forward and reverse reactions are equal, resulting in no net change in the concentration of reactants and products over time. It's represented by the double arrows (\rightleftharpoons) in the chemical equations. For carbonic acid, both dissociation steps achieve their own chemical equilibrium. This means that at any point, a dynamic balance is maintained between carbonic acid, bicarbonate ions, carbonate ions, and hydronium ions. The equilibrium constant (\(K_a\)) for these reactions is crucial for determining the extent of dissociation and the concentration of each species in solution.

Proton donation is a fundamental process in acid-base chemistry. It involves the transfer of a proton (\(H^+\)) from the acid to another substance, usually water, resulting in the formation of a hydronium ion (\(H_3O^+\)) in aqueous solutions. Carbonic acid displays this behavior successively in two stages; first, by donating a proton to water and creating bicarbonate and a hydronium ion, and second, by the bicarbonate ion acting as an acid itself and donating a proton to water to form carbonate. This sequential proton donation is characteristic of diprotic acids, and it provides insights into their buffering capacity and role in pH regulation.

The bicarbonate ion (\(HCO_3^-\)) plays a crucial role as an intermediate in the dissociation of carbonic acid. It is produced in the first stage of dissociation and represents a balance between the undissociated carbonic acid and the dissociated carbonate ion. Bicarbonate serves not only as the conjugate base of carbonic acid but also as an acid in its own right, capable of donating a proton to form the carbonate ion. It is a pivotal component in the body's buffering system, helping to maintain stable pH levels in blood and other biological fluids.

The carbonate ion (\(CO_3^{2-}\)) is the result of the complete dissociation of carbonic acid after both protons have been donated. It is a polyatomic ion with a 2- charge that acts as the conjugate base of the bicarbonate ion. The presence of the carbonate ion is essential in various geological and biological processes, such as the formation of limestone and the regulation of the acid-base balance in organisms. It is also a significant component of the Earth's carbon cycle, where it participates in reactions that sequester atmospheric carbon dioxide.

The hydronium ion (\(H_3O^+\)), often represented simply as (\(H^+\)) in aqueous solutions, is formed through the association of a proton with a water molecule. This ion is central to acid-base chemistry and is a measure of acidity in water. In the dissociation of carbonic acid, hydronium ions are produced during both steps as protons are donated to water molecules. The concentration of hydronium ions is what is measured when determining the pH of a solution; the higher the concentration of hydronium ions, the lower the pH (more acidic) the solution.