Question

Calculate the conditional formation constant of the EDTA complex of Al³⁺ in a solution buffered to pH = 3.0 Answer to 3 significant digits.

Answer 1

Consider complex formation reaction, Al ³⁺ + Y ^4-$\rightleftharpoons$ [ Al Y ^-1]

The equilibrium constant for above reaction is called formation constant and is given as,

K f = [ Al Y ^-1] / [Al ³⁺ ] [Y ^4-]

The conditional formation constant is given as, K ' f = $\alpha$_Y 4- K f

At pH = 3.0 , $\alpha$_Y 4- = 2.1 $\times$ 10 ^-11

From literature, log K f = 16.4

$\therefore$ Conditional formation constant ( K ' f ) = ( 2.1 $\times$ 10 ^-11 ) 10 ^16.4 = 5.27 $\times$ 10 ⁵

ANSWER : K ' f = 5.27 $\times$ 10 ⁵