A Thermodynamic Study of Chromotropico‐Titanium(III) Complex from Spectrophotometric Measurements

The formation of 1 : 2 titanium(III) complex with chromotropic acid (4, 5‐dihydroxy‐2, 7‐naphthalene‐disulfonic acid) was observed by spectrophotometric measurements at various ionic strengths. An expression, [Ti(III)]/ D =1/Δϵ + α H 2 +/ K Δϵ[H 2 R 2− ] 2 , was derived for the determination of the formation constant, K =7.2×10 2 liter 2 mol −2 for the Ti(III).(HR) 2 ion in the p H range of 1.3–1.8 at constant ionic strength, I =0.2 M , at 25° C . The thermodynamic data for the reaction, Ti(III)+2H 3 R 2− =Ti(III) (HR) 2 +2H + , were calculated to be ΔG ° = −16 k J mol −1 ΔH ° = 18 k J mol −1 , ΔS ° = 110 JK −1 mol −1 , at 25° C .