Consider the oxalate ion, C2O4^-2.

Consider the oxalate ion, C2O4^-2. Draw the Lewis structure, including all equivalent resonance structures. Are all carbon-oxygen bonds the same in this ion? If so, give the bond order. If not, give the bond order for each unique bond. b) The oxalate ion is the anion of oxalic acid, H2C2O4, an oxo-acid. Oxalic acid is found in rhubarb leaves and is toxic. Draw the Lewis structure for oxalic acid. Are all carbon-oxygen bonds the same in this ion? If so, give the bond order. If not, give the bond order for each unique bond. c) Consider HC2O4^-. Draw the Lewis structure for oxalic acid. Are all carbon-oxygen bonds the same in this molecule? If so, give the bond order. If not, give the bond order for each unique bond

The Correct Answer and Explanation is:

a) Lewis Structure of Oxalate Ion (C₂O₄²⁻)

Oxalate ion has the formula C₂O₄²⁻, with two carbon atoms and four oxygen atoms. Each carbon atom forms three bonds: one to another carbon and two to oxygens. The ion carries a total charge of −2.

There are two major resonance structures where the negative charges are delocalized among the oxygen atoms. Each carbon is double-bonded to one oxygen and single-bonded to another, but in different patterns.

Resonance Structures:

mathematicaCopyEdit  O⁻       O
   \       //
    C — C
   //       \
  O        O⁻

  O        O⁻
   \\       /
    C — C
   /       \\
 O⁻        O

Bond Order Analysis:

The carbon-oxygen bonds alternate between single and double in the resonance structures, but resonance causes the actual bond lengths to be equalized. Since each C—O bond is either a single or double bond in different structures, and there are 4 C—O bonds with 2 double bonds total across structures, the average bond order is 1.5. Therefore, all C—O bonds are equivalent due to resonance, with a bond order of 1.5.

b) Lewis Structure of Oxalic Acid (H₂C₂O₄)

Oxalic acid has two carboxylic acid groups: HO–C(=O)–C(=O)–OH.

Structure:

scssCopyEditHO—C(=O)—C(=O)—OH

Each carbon is double bonded to one oxygen and single bonded to a hydroxyl group (–OH). There are no equivalent resonance structures affecting the entire molecule like in the oxalate ion.

Bond Order Analysis:

• Each carbon has one C=O (double bond) and one C–OH (single bond).
• So, not all carbon–oxygen bonds are the same.
• Bond order for C=O is 2, and for C–OH is 1.

c) Lewis Structure of Hydrogen Oxalate Ion (HC₂O₄⁻)

This is the monoanion of oxalic acid. It contains one protonated carboxylic acid (COOH) and one deprotonated carboxylate (COO⁻) group.

Structure:

mathematicaCopyEditHO—C(=O)—C(–O⁻)=O

The carboxylate group (COO⁻) has resonance between its two oxygen atoms, while the carboxylic acid group (COOH) does not.

Bond Order Analysis:

• In COOH group: C=O is bond order 2, C–OH is bond order 1.
• In COO⁻ group: both C–O bonds are resonance-stabilized and have bond order 1.5.

So, not all carbon–oxygen bonds are the same in HC₂O₄⁻:

• One C=O: bond order 2
• One C–OH: bond order 1
• Two C–O in COO⁻ group: bond order 1.5 each.