Question

For each pair of molecules or ions, select the stronger base and write its Lewis structure. (a) \(\mathrm{CH}_{3} \mathrm{~S}^{-}\)or \(\mathrm{CH}_{3} \mathrm{O}^{-}\) (b) \(\mathrm{CH}_{3} \mathrm{NH}^{-}\)or \(\mathrm{CH}_{3} \mathrm{O}^{-}\) (c) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\)or \(\mathrm{OH}^{-}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\)or \(\mathrm{H}^{-}\) (e) \(\mathrm{NH}_{3}\) or \(\mathrm{OH}^{-}\) (f) \(\mathrm{NH}_{3}\) or \(\mathrm{H}_{2} \mathrm{O}\) (g) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\)or \(\mathrm{HCO}_{3}^{-}\) (h) \(\mathrm{HSO}_{4}^{-}\)or \(\mathrm{OH}^{-}\) (i) \(\mathrm{OH}^{-}\)or \(\mathrm{Br}^{-}\)

Short answer

Question: Identify the stronger base in each pair and provide the Lewis structure for the stronger base. (a) CH3S- or CH3O- - Stronger base: CH3S- - Lewis structure: ``` S / \ H - C - H | H ``` (b) CH3NH- or CH3O- - Stronger base: CH3NH- - Lewis structure: ``` N / \ H - C - H | H ``` (c) CH3COO- or OH- - Stronger base: OH- - Lewis structure: ``` O / \ H ``` (d) CH3CHO- or H- - Stronger base: H- - Lewis structure: ``` H ``` (e) NH3 or OH- - Stronger base: OH- - Lewis structure: ``` O / \ H ``` (f) NH3 or H2O - Stronger base: NH3 - Lewis structure: ``` N / \ H H \ H ``` (g) CH3COO- or HCO3- - Stronger base: CH3COO- - Lewis structure: ``` O O \\ / C - O - C - H C - C - O - H / \ H H ``` (h) HSO4- or OH- - Stronger base: OH- - Lewis structure: ``` O / \ H ``` (i) OH- or Br- - Stronger base: OH- - Lewis structure: ``` O / \ H ```

Step-by-step solution

Identify the stronger base

As sulfur is larger and less electronegative than oxygen, \(\mathrm{CH}_{3} \mathrm{S}^{-}\) is more likely to donate electrons and therefore is a stronger base.

Lewis structure for CH3S-

The Lewis structure can be drawn as: ``` S / \ H - C - H | H ``` with a lone pair of electrons on the sulfur atom. (b) \(\mathrm{CH}_{3} \mathrm{NH}^{-}\) or \(\mathrm{CH}_{3} \mathrm{O}^{-}\)

Identify the stronger base

Since nitrogen is less electronegative than oxygen, \(\mathrm{CH}_{3} \mathrm{NH}^{-}\) is a stronger base.

Lewis structure for CH3NH-

The Lewis structure can be drawn as: ``` N / \ H - C - H | H ``` with a lone pair of electrons on the nitrogen atom. (c) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) or \(\mathrm{OH}^{-}\)

Identify the stronger base

Oxygen in the hydroxide ion, \(\mathrm{OH}^{-}\), is less hindered than the oxygen in the acetate ion, \(\mathrm{CH}_{3} \mathrm{COO}^{-}\), which has resonance structures. This makes \(\mathrm{OH}^{-}\) a stronger base.

Lewis structure for OH-

The Lewis structure can be drawn as: ``` O / \ H ``` with a lone pair of electrons on the oxygen atom. (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\) or \(\mathrm{H}^{-}\)

Identify the stronger base

The hydride ion, \(\mathrm{H}^{-}\), is a very strong base due to its small size and inability to stabilize a negative charge. It is a stronger base than \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}\).

Lewis structure for H-

The Lewis structure can be drawn as: ``` H ``` with a lone pair of electrons on the hydrogen atom. (e) \(\mathrm{NH}_{3}\) or \(\mathrm{OH}^{-}\)

Identify the stronger base

Between the two molecules, the hydroxide ion, \(\mathrm{OH}^{-}\), is a stronger base due to its negative charge.

Lewis structure for OH-

As mentioned before, the Lewis structure can be drawn as: ``` O / \ H ``` with a lone pair of electrons on the oxygen atom. (f) \(\mathrm{NH}_{3}\) or \(\mathrm{H}_{2} \mathrm{O}\)

Identify the stronger base

Since nitrogen is less electronegative than oxygen, ammonia (\(\mathrm{NH}_{3}\)) is a stronger base than water (\(\mathrm{H}_{2} \mathrm{O}\)).

Lewis structure for NH3

The Lewis structure can be drawn as: ``` N / \ H H \ H ``` with a lone pair of electrons on the nitrogen atom. (g) \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) or \(\mathrm{HCO}_{3}^{-}\)

Identify the stronger base

The acetate ion, \(\mathrm{CH}_{3} \mathrm{COO}^{-}\), is a stronger base due to its resonance structures, which stabilize the negative charge more effectively than in the bicarbonate ion, \(\mathrm{HCO}_{3}^{-}\).

Lewis structure for CH3COO-

The Lewis structure can be drawn as: ``` O O \\ / C - O - C - H C - C - O - H / \ H H ``` with alternating single and double bonds between the carbons and oxygens and negative charges on the oxygen atoms. (h) \(\mathrm{HSO}_{4}^{-}\) or \(\mathrm{OH}^{-}\)

Identify the stronger base

Between these two, the hydroxide ion (\(\mathrm{OH}^{-}\)) is a stronger base because it is free to donate electrons more easily than the bisulfate ion (\(\mathrm{HSO}_{4}^{-}\)) which has a larger, more complex structure.

Lewis structure for OH-

As mentioned earlier, the Lewis structure can be drawn as: ``` O / \ H ``` with a lone pair of electrons on the oxygen atom. (i) \(\mathrm{OH}^{-}\) or \(\mathrm{Br}^{-}\)

Identify the stronger base

In this case, the hydroxide ion (\(\mathrm{OH}^{-}\)) is a stronger base because the oxygen atom is more electron-rich and able to donate electrons more effectively than the bromide ion (\(\mathrm{Br}^{-}\)).

Lewis structure for OH-

Once again, the Lewis structure can be drawn as: ``` O / \ H ``` with a lone pair of electrons on the oxygen atom.