Question

A solution contains [Ba 2+] = 5.0 x10^-5; [Ag+]=3.0E-5, and [Zn+]=2.0E-7; Sodium Oxalate is slowly added so that [C2O4 2-] increase: Ksp of BaC2O4=1.5E-8 Ksp of ZnC2O4=1.35E-9 Ksp of Ag2C2O4= 1.1E-11 what is the concentration of the 1st cation when the 2nd cation just begin to ppt?

A)1.3E-6 B)2.2E-6 C)5.0E-5 D)1.35E-9 E)1.1E-11 Please write the explanation too, thank you!

Answer 1

data :

The first to precipitate will be the first that saturate the disolution.We need to calculate this from the Ksp Equation:

sustituing values :

from the eq (1) is calculated [C2O4]BA :

The same calcule is realized for [C2O4]Zn and [C2O4]Ag :

he first to precipitatte will be who need the lowest concentration of [C2O2] .So , the first to precipitate is [Ba+].

Now, to calculate the [Ba ] when tthe 2nd cation just begin to precipitate, we need to know that the 2nd cation is the [Zn] , because has the lowestt concentration of C2O4 between [Zn] and [Ag], for this at this momento

[C2O4]= 6,75x10^(-3) ( Just the concentration to begin the precipitate of Zn).

To calculate [Ba+] :

so, THE ANSWER IS B) 2,2E-6