Question

A 110.0 mL sample of 0.040 M Ca2+ is titrated with 0.040 M EDTA at pH 9.00. The value of logKf for the Ca2+−EDTA complex is 10.65 and the fraction of free EDTA in the Y4− form, ????Y4− , is 0.041 at pH 9.00. What is K′f , the conditional formation constant, for Ca2+ at pH 9.00?

Answer 1

Answer : The conditional formation constant is
`1.83* 10^9`

Explanation :

First we have to calculate the formation constant.

As we are given that:

`\log k_f=10.65`

`k_f=10^(10.65)`

`k_f=4.47* 10^(10)`

Thus, the formation constant is
`4.47* 10^(10)`

Now we have to calculate the conditional formation constant.

The expression used as:

`k'_f=\alpha_y^+* k_f`

where,

`k'_f` = conditional formation constant = ?

`\alpha_y^+` = activity coefficient at pH 9.00 = 0.041

`k_f` = formation constant =
`4.47* 10^(10)`

Now put all the given values in the above expression, we get:

`k'_f=(0.041)* (4.47* 10^(10))`

`k'_f=1.83* 10^9`

Therefore, the conditional formation constant is
`1.83* 10^9`