Questions: 19. A Lewis structure for the oxalate ion is shown here. Select the best predictions for the angles labeled A, an O-C-O angle and B, a C-C-O angle. (a) A=120° and B=120° (b) A=109.5° and B=109.5° (c) A=109.5° and B=120° (d) A=120° and B=109.5°

19. A Lewis structure for the oxalate ion is shown here. Select the best predictions for the angles labeled A, an O-C-O angle and B, a C-C-O angle.
(a) A=120° and B=120°
(b) A=109.5° and B=109.5°
(c) A=109.5° and B=120°
(d) A=120° and B=109.5°

Transcript text: 19. A Lewis structure for the oxalate ion is shown here. Select the best predictions for the angles labeled A, an O-C-O angle and B, a C-C-O angle. (a) $\underline{A}=120^{\circ}$ and $\underline{B}=120^{\circ}$ (b) $\underline{\mathrm{A}}=109.5^{\circ}$ and $\underline{B}=109.5^{\circ}$ (c) $\underline{A}=109.5^{\circ}$ and $\underline{B}=120^{\circ}$ (d) $\underline{A}=120^{\circ}$ and $\underline{B}=109.5^{\circ}$

Solution

Solution Steps

Step 1: Understanding the Geometry of the Oxalate Ion

The oxalate ion, $\text{C}_2\text{O}_4^{2-}$, consists of two carbon atoms and four oxygen atoms. The Lewis structure typically shows each carbon atom double-bonded to one oxygen and single-bonded to another oxygen, with the two carbon atoms connected by a single bond.

Step 2: Analyzing the O-C-O Angle (Angle A)

The O-C-O angle involves a carbon atom bonded to two oxygen atoms. In the oxalate ion, the carbon atom is sp$^2$ hybridized due to the presence of a double bond with one of the oxygens. This hybridization results in a trigonal planar geometry around the carbon atom, leading to an O-C-O bond angle of approximately $120^\circ$.

Step 3: Analyzing the C-C-O Angle (Angle B)

The C-C-O angle involves a carbon atom bonded to another carbon and an oxygen atom. The carbon atom is also sp$^2$ hybridized, maintaining a trigonal planar geometry. Therefore, the C-C-O bond angle is also approximately $120^\circ$.