Oxalic acid (H2C204) has the following structure

Oxalic acid (H2C204) has the following structure:

An oxalic acid solution contains these species in varying concentrations: H2C2O4, HCO CO, and H+.
(a
) Draw Lewis structures of HCO and CO. (b) Which of the four species listed here can act only as acids, which can act only as bases, and which can act as both acids and bases?

The Correct Answer and Explanation is :

(a) Lewis Structures of HCO and CO

1. HCO (Formate ion): The formula HCO represents the formate ion, which is the conjugate base of formic acid (HCOOH). The Lewis structure of HCO (formate ion) is:

   H-C=O
      |
      O

In this structure:

• The carbon (C) is bonded to both a hydrogen (H) and a double-bonded oxygen (O).
• The other oxygen (O) is bonded to carbon with a single bond, carrying a negative charge. This negative charge is delocalized over both oxygen atoms due to resonance.

1. CO (Carbon monoxide): The formula CO represents the molecule carbon monoxide. Its Lewis structure is:

   :C≡O:

In this structure:

• Carbon (C) is triple-bonded to oxygen (O), and both atoms have lone pairs.
• The triple bond between C and O creates a very strong bond and results in a molecule with a linear geometry.
• The carbon atom has two lone pairs, and oxygen has two lone pairs as well, giving each atom an octet.

(b) Acid-Base Behavior of Species

1. H2C2O4 (Oxalic acid): This species can act as an acid because it can donate a proton (H+). Oxalic acid has two carboxylic acid groups (-COOH) that can dissociate to release protons, which makes it a typical diprotic acid. Hence, oxalic acid is an acid.
2. HCO (Formate ion): The formate ion (HCO) can act as a base because it is the conjugate base of formic acid. It can accept a proton to regenerate formic acid. Hence, the formate ion acts as a base.
3. CO (Carbon monoxide): Carbon monoxide is a neutral molecule, but it can act as a Lewis base due to the lone pairs of electrons on the carbon atom. It can donate these electrons to form coordination complexes with metal ions, making it a base.
4. H+ (Proton): The proton (H+) is a classic example of an acid, as it can donate itself (a proton) to other species, thereby acting as an acid.

Conclusion on Acid-Base Behavior:

• Acid-only: H2C2O4 (Oxalic acid) and H+ (proton).
• Base-only: HCO (Formate ion) and CO (carbon monoxide, when considering Lewis base behavior).
• Both acid and base: The formate ion (HCO) could be considered amphoteric because it can act as both an acid and a base depending on the situation (it can donate or accept protons).