Solving for electron activity given pH and ratio of redox elements

[peeballs]

Homework Statement

What is the apparent pO2 (atm) in equilibrium with a pE governed by the sulfate/sulfide redox buffer when
(SO4
2-) = 10x (HS-) at paH 8.2? Use constants from Table 8.6a, pg. 465, assume I=0.

Relevant Equations

K = Products/Reactants

I've written out the half reaction

8e^- + 9H⁺ + SO₄^2- = HS^- + 4H₂O

and I know the logK = 4.25 (that's the constant mentioned in the prompt)

I've written out the equilibrium statement of 10^4.25 = ([x^1/8]*[H2O^1/2])/([10x^1/8]*[e-]*[(10^-8.2)^9/8]

However, from there, it seems like I have two unknowns - the X, and the e-, which I'm solving for. I don't know of any formulas that would be useful here and I was specifically told to use this expression to solve it.

Thanks

 

[Borek]

You sure x is an unknown, and not a multiplication sign?

 

[peeballs]

You sure x is an unknown, and not a multiplication sign?

Yes, but you managed to find me on a different forum and explain why I was having a brainfart so it all works out.