Conductometric Studies of Calcium Ions with Kryptofix 221 in Mixed MeOH-DMF Solvents at Different Temperatures

Abstract

On using conductometric technique, the apparent association constant (KA) of Ca (NO3)2 were measured in mixed MeOH-DMF mixed solvents at 0, 20, 40 , 60 ,80 and 100% MeOH (by volume) and different temperatures (298.15, 303.15, 308.15 and 313.15K) in absence and presence of . Kryptofix- 221 [4, 7, 13, 16, 21- pentaoxa-1.10-diazo-bicyclo (8,8,5) tricosane]. From the experimental results, the molar conductivities (∧) were calculated and limiting molar conduc- tivities (∧0) were calculated by using Shedlovsky and Fouss – Kraus extrapolation methods. The molar solvated (∨), Van der Waals (∨w) and electrostriction (∨e) were evaluated. The association constants KA for Ca(NO3)2 were calculated by using simple equation derived from Ostwald, Arrhenius and Fuoss-Shedlovsky theories. From the association constants the dif- ferent thermodynamic parameters were evaluated and the results obtained were discussed. The free energy of association ( ∆GA ), free energy necessary for complexation ( ∆Gcomplex ) and enthalpy (ΔH) were determined. It was concluded that the maximum complexation between calcium ions and Kryptofix-221 were by using 80% and 100%. MeOH in the mixtures. Where as the least complexing ability at 40% and 60% by volume of MeOH .This work give data can help for the analytical determination of calcium in blood and water samples.