2-Pyridinealdehyde-2'-hydroxynaphthylamine as an indicator in complexometric titration of copper(II)

• Published in: Bunseki kagaku Vol. 30; no. 11; pp. 731 - 736
• Main Authors: ISAGAI, Kazuyo, ISAGAI, Kiyoharu, YAMASAKI, Kazue
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Science and Technology Agency 1981
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.30.11_731

2-Pyridinealdehyde-2'-hydroxynaphthylamine(PHN) which is hardly soluble in water but soluble in alcohol has been used for the spectrophotometric determination of copper(II). Since PHN forms water soluble, reddish-orange complex with copper(II) and the color of this copper complex diminishes by addition of EDTA solution, use of PHN as an indicator for the titration of copper(II) with EDTA solution is proposed. At first, the acid dissociation constants of PHN were determined at 25°C, μ=0.1, and pK1 and pK2 were obtained to be 3.75 and 8.25, respectively. Also the formation constant of the copper complex was estimated as 5.0 × 109. Therefore, PHN can be used as an indicator in the pH range 3.54.5. The color at the end point in titration turns from reddish-orange to light blue and the equivalence point was indicated sharply. PHN may be used as an indicator like as the familiar reagents such as 1-(2-pyridylazo)-2-naphthol(PAN), 1-(2-thiazolylazo)-2-naphthol (TAN) and 4-(2-thiazolylazo)-resorcinol(TAR). The conditional formation constants of copper PHN complex and copper EDTA complex at pH 4 were evaluated as 1.8 × 105 and 2.3 × 1010, respectively. Using these values, the relationship between the ratio of metal titrated and the change in color was obtained. The result shows that color change is visually sharp at the end point when 2 to 4 drops of 0.5 % PHN solution in alcohol are added to the sample solution. The order of interference by diverse ions is iron> zinc> cadmium> nickel> cobalt.