From esters

Carboxylic acids can be obtained from esters by EITHER of two hydrolysis routes. (a) ACID hydrolysis: an ester heated with a dilute mineral acid (dilute HCl or dilute H2SO4) gives the corresponding carboxylic acid, along with the alcohol it was esterified from -- e.g. R-CO-O-R' + H2O, with dilute H2SO4 and heat, gives R-COOH + R'-OH. (b) ALKALINE hydrolysis: an ester heated instead with a dilute alkali (dilute NaOH or dilute KOH) forms a water-soluble sodium or potassium salt of the acid (the carboxylate) directly, rather than the free acid; for example, methyl propanoate (H5C2-CO-O-CH3) with dilute NaOH and heat gives sodium propanoate (H5C2-COO(-)Na(+)) + methanol. Acidifying that carboxylate salt afterwards with concentrated HCl then liberates the free acid: sodium propanoate + H2O, with conc. HCl, gives propanoic acid + NaOH. Because the sodium/potassium salts of HIGHER fatty acids specifically are known as soaps, this alkaline-hydrol …