3-Alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones 2 react with acyl halides such as chloroacetyl chloride, dichloroacetyl chloride and isobutyryl chloride to give the corresponding 3-alkyl(aryl)-4-chloroacetylamino-4,5-dihydro-1H-1,2,4-triazol-5-ones 3, 3-alkyl(aryl)-4-(dichloroacetylamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones 4 and 3-alkyl(aryl)-4-isobutyrylamino-4,5-dihydro-1H-1,2,4-triazol-5-ones 5, respectively. The newly synthesized compounds have been characterized by elemental analyses, IR, H-1 NMR, C-13 NMR and UV spectral data. In addition, all ten new compounds are titrated potentiometrically with tetrabutylammonium hydroxide in four different non-aqueous solvents such as isopropyl alcohol, tert-butyl alcohol, acetonitrile and N,N-dimethylformamide. The half neutralization potential values and the corresponding pK(a) values have been determined for all the cases. Thus, the effects of solvents and molecular structure upon acidity are investigated.