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 [Cu x Hg|CuCl 2( 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 ( K 1 and K 2) and the degree of dissociation ( α 1 and α 2) by iterative procedures. The standard cell potential ( E°) and the mean activity coefficient ( γ ±) of CuCl 2 were also determined. The E° data were next used to evaluate the Gibbs energy of transfer ( Δ G tr ∘ ) of CuCl 2 from water to dilute aqueous solutions of the amino/carboxylic acids. The negative Δ G tr ∘ values suggested that these acids act as potential corrosion inhibitors. The magnitudes of Δ G tr ∘ values show that the amino acids act as better corrosion inhibitors towards copper than the aliphatic carboxylic acids.