The spectral behavior of some Schiff base compounds derived from 2-((2,4-dihydroxyphenyl) (hydroxy)methyl)-2-
phenylhydrazono)propanal,2-(2-(hydroxy(2-hydroxy-4-methoxyphenyl)methyl)-2-phenylhydrazono)propanal,3-(2-(hydroxy
(2-hydroxy-4-methoxyphenyl)methyl)-2-phenylhydrazono)butan-2-one and 2-(-(2,4-dihydroxybenzylidene) hydrazono)-1,2-
diphenylethanone to investigate the acid ionization constants (pKH) of these ligands using Half-height method and Modified 
limiting absorbance method. A series of new metal chelates of Co(II), Cu(II), Gd(III), Sm(III) and Tb(III) with Schiff base 
ligands derived from condensation of glyoxal, biacetyl or benzyl bishydrazone with 2,4 – dihydroxybenzaldhyde and 4-
methoxysaliycaldhyde in ethanol and characterized via potentiometric titrations. Stability constants of these metal complexes 
were determined using a potentiometric method by calculating the values of n̅ A, n̅ and pL and found in the order 
Co(II)