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Why is formic acid stronger than acetic acid?
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carboxylic acid
Alcohols may be oxidized to give aldehydes, ketones, and carboxylic acids. The oxidation of organic compounds generally increases the number of bonds from carbon to oxygen, and it may decrease the number of bonds to hydrogen.
Formic acid is stronger than acetic acid because of the influence of the methyl group attached to the carboxyl group in acetic acid.
In carboxylic acids, the acidity is determined by the stability of the resulting carboxylate ion. Substituents attached to the carbon atom can affect this stability through the inductive effect:
- Electron-donating groups: These groups destabilize the carboxylate ion, thereby decreasing the acidity of the parent acid. The methyl group (–CH₃) in acetic acid is generally considered electron-donating.
- Electron-withdrawing groups: These groups increase acidity by stabilizing the carboxylate ion.
Because the methyl group in acetic acid donates electrons, it destabilizes the carboxylate ion compared to the hydrogen atom found in formic acid. Consequently, acetic acid is approximately 10 times weaker as an acid than formic acid.1