Carboxylic acids (RCOOH) are the most acidic common organic functional group, with typical pKa values of 4–5 for simple members. Their high acidity results from resonance stabilization of the carboxylate ion (RCOO–), where the negative charge is delocalized equally over two equivalent C–O bonds of bond order 1.5. Electron-withdrawing halogen substituents stabilize the carboxylate further and increase acidity, while electron-donating alkyl groups destabilize it and decrease acidity. Formic acid (pKa 3.75) is stronger than acetic acid (pKa 4.76) because the H atom in HCOOH has no +I inductive effect, unlike the –CH3 in acetic acid. The four principal preparation methods are oxidation of primary alcohols/aldehydes, Grignard reaction with CO2, nitrile hydrolysis, and ester saponification. The HVZ reaction $\frac{X2}{Red P}$ alpha-halogenates carboxylic acids but requires an alpha-hydrogen, excluding formic acid and benzoic acid. Fischer esterification is a reversible acid-catalyzed condensation producing an ester and water; saponification by NaOH is irreversible and yields the carboxylate salt. SOCl2 is the preferred reagent for acyl chloride formation because both byproducts (SO2 and HCl) are gaseous, simplifying purification. LiAlH4 reduces carboxylic acids to primary alcohols, while NaBH4 is too mild for this transformation and gives no reaction with RCOOH. Kolbe electrolysis oxidizes carboxylate anions at the anode to form symmetrical alkanes and CO2, while soda lime decarboxylation converts sodium carboxylate salts to alkanes with one fewer carbon.