Oxalic acid (H2 C2 O4) has the following structure: An...

Oxalic acid $\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right)$ has the following structure: An oxalic acid solution contains the following species in varying concentrations: $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}, \mathrm{HC}_{2} \mathrm{O}_{4}^{-},$ $\mathrm{C}_{2} \mathrm{O}_{4}^{2-},$ and $\mathrm{H}^{+} .$ (a) Draw Lewis structures of $\mathrm{HC}_{2} \mathrm{O}_{4}^{-},$ and $\mathrm{C}_{2} \mathrm{O}_{4}^{2-} .$ (b) Which of the above four species can act only as acids, which can act only as bases, and which can act as both acids and bases?

Oxalic acid $\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right)$ has the following structure:
An oxalic acid solution contains the following species in varying concentrations: $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}, \mathrm{HC}_{2} \mathrm{O}_{4}^{-},$ $\mathrm{C}_{2} \mathrm{O}_{4}^{2-},$ and $\mathrm{H}^{+} .$ (a) Draw Lewis structures of $\mathrm{HC}_{2} \mathrm{O}_{4}^{-},$ and $\mathrm{C}_{2} \mathrm{O}_{4}^{2-} .$ (b) Which of the above four species can act only as acids, which can act only as bases, and which can act as both acids and bases?

Key Concepts

Conjugate Acid–Base Pairs

Conjugate acid–base pairs are related chemical species that transform into each other by the gain or loss of a proton. When an acid donates a proton, it forms its conjugate base, and when a base accepts a proton, it forms its conjugate acid. This interplay is fundamental in the analysis of acid–base equilibria, especially in systems involving polyprotic acids.

Amphoteric Behavior

Amphoteric substances are those that can act either as acids or as bases depending on the reaction environment. This dual capability is significant in acid–base chemistry as it explains how certain species can both donate and accept protons, influencing the overall behavior of the solution.

Brønsted–Lowry Acid–Base Theory

The Brønsted–Lowry acid–base theory characterizes acids as proton donors and bases as proton acceptors. This concept is central to understanding the behavior of different species in solution—the ability of a species to donate or accept a proton determines whether it can act as an acid, a base, or both.

Lewis Structures

Lewis structures are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist. They are used to represent molecules’ electronic structures, giving insight into bond formation, geometry, and potential sites for reactivity, which is crucial when analyzing species such as conjugate bases derived from acid dissociation.

Polyprotic Acids

Polyprotic acids are acids that can donate more than one proton (H?) in solution through successive dissociation steps, each with its own equilibrium constant. Understanding polyprotic behavior is important as it explains the presence of multiple species in solution, each with differing acid-base properties.

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