[Danial]

Using 0.000001 as a critera of quantative removal.
Is it feasible to use SO₄^2- to seperate Ba²⁺ (0.30M) and Sr²⁺ (0.050M) in a solution.
[Ba²⁺][SO₄^2-]=1.1x10^-10 so its less soluble
[Sr²⁺][SO₄^2-]=3.2x10^-7

soo i went [Ba²⁺] = 0.000001 so [SO₄^2-] = 1.1x10^-4  (1)

then

[Sr²⁺] = 0.050 so [SO₄^2-] = 6.4x10^-6   (2)

and because (1) is greater than (2) it is not feasible to separate them with SO₄^2-

is that correct? do i need to use the given [Ba²⁺]=0.30 ?

Edit: formatting corrected

[Danial]

Sorry the Br concentrations actually mean Ba i got confused but the math is still the same
is this process correct? the example i followed had the concentrations of both cations the same
so is it wrong that i don't include the given concentration of Ba ?

[Stclair]

Don't you have to determine the ration between the two concentrations?
Br and Sr ?

[Borek]

You need to calculate ratio of concentrations AFTER the separation.

In this particular case seems like it means ratio of concentrations of Ba²⁺ and Sr²⁺ when Sr²⁺ starts to precipitate.

[Danial]

[Sr²⁺] = 0.050 so [SO₄^2-] = 6.4x10^-6 when it starts to precipitate?

[Ba²⁺] = 1.1x10^-10 / 6.4x10^-6 = 1.72x10^-5

Ratio between them Br/Sr = 3.44x10^-4

Is that what you mean?

[Borek]

Seems like.

[Danial]

Oh okay cool.
But im kind of confused, what do i use that ratio for, do i times it by the concentration i initially calculated for a 1x10^-6 criteria for quantitative removal?

[Borek]

What is definition of the criteria you are using? What does the number tell?

[Danial]

It means that analyte has been quantitatively removed, that there is only 1 part of the analyte in 1000000 left in the solution.
I was following an example given in my book, but that example had both the analytes at the same concentration, and this question has the analytes with different concentrations, so im just kind of confused of how to get the answer.

[Borek]

It means that analyte has been quantitatively removed, that there is only 1 part of the analyte in 1000000 left in the solution.

OK, I was partially wrong. You have to compare concentration of Ba²⁺ before and after the precipitation, concentration of Sr²⁺ is used only to calculate when does the Ba²⁺ removal end.

[Danial]

Ohhh ok i think i get this now
i was just reading over the book
so i initially go

[Ba²⁺]/1000000

thennnnn solve the problem similar to before

[Ba²⁺][SO₄^2-]=1.1x10-10
find [SO₄]

Then compare it to the concentration of SO₄ found when using 0.05 M Sr
I thinkkk thats what I have to do



Ok so i tried that and i still get similar answers, 3 out of the 4 questions are "not feasible" and the one that is feasible has both the concentrations of the cations equal, soo I kind of think im missing somthing.
Is all that stuff i did up there what you meant? I'm not sure how to compare the Ba after the precipitation.
Or would i go like, calculate the [SO₄] when [Ba] = 1x10^-6, then calculate [SO₄] when [Ba] = 0.030M, then compare both those [SO₄]?