Carboxylic acid - Physical properties - Acidity

Carboxylic acids are typically weak acids, meaning that they only partially dissociate into H+ cations and RCOO− anions in neutral aqueous solution. For example, at room temperature, in a 1-molar solution of acetic acid, only 0.4% of the acid molecules are dissociated. Electronegative substituents give stronger acids.

Reference 1: pKa.

Reference 2: Formic acid (HCOOH), Acetic acid (CH3CO2H), Chloroacetic acid (CH2ClCO2H), Dichloroacetic acid (CHCl2CO2H), Trichloroacetic acid (CCl3CO2H), Trifluoroacetic acid (CF3CO2H), Oxalic acid (HO2CCO2H) and Benzoic acid (C6H5CO2H).

Source: http://en.wikipedia.org/wiki/Carboxylic_acid