Electrochemical behavior of p-benzoquinone (Q), hydroquinone (H(2)Q) and quinhydrone complex (QH) have been investigated in aqueous unbuffered solutions. The results revealed that in unbuffered solution the half wave potential of hydroquinone has a significant difference with quinone's half wave potential. It shown that, added acid in an unbuffered solution of Q, give rise to a new reduction peak at a more positive potential than original reduction peak of Q. The half-peak potential of this new peak is dependent on acidity of added acid (pK(a)) and its height is proportional to the acid concentration. Also, added base in an unbuffered solution of H(2)Q, give rise to a new oxidation peak at a more negative potential than original oxidation peak of H(2)Q. The half-peak potential of this new peak is dependent on basicity of added base (pK(b)) and its height is proportional to the base concentration. This paper shows new perspectives for a known system in aqueous unbuffered solutions, by means of voltammetric responses that can be exploited for the electrochemical investigation of non electroactive species such as HPO42-, HCO3- or CH3COOH.
