Thermodynamic studies on corrosion inhibition of aqueous solutions of amino/carboxylic acids toward copper by EMF measurement

Electromotive force (E) measurements were made on an electrochemical cell [CuxHg|CuCl2(m) in a solvent S|AgCl-Ag] (where S is a dilute aqueous solution (0.01 m) of amino acid (glycine, alanine, methionine and glutamic acid) or aliphatic carboxylic acid (formic acid, acetic acid, n-butyric acid and glutaric acid)) at 30 °C. These measured E values were used to compute the dissociation constants (K1 and K2) and the degree of dissociation (α1 and α2) by iterative procedures. The standard cell potential (E°) and the mean activity coefficient (γ±) of CuCl2 were also determined. The E° data were next used to evaluate the Gibbs energy of transfer (ΔGtr∘) of CuCl2 from water to dilute aqueous solutions of the amino/carboxylic acids. The negative ΔGtr∘ values suggested that these acids act as potential corrosion inhibitors. The magnitudes of ΔGtr∘ values show that the amino acids act as better corrosion inhibitors towards copper than the aliphatic carboxylic acids.