General Chem Destroyer # 86

[tpwelie34]

Hi guys, after setting up my ice table and everything , I get the equation: Ksp = [Fe][OH]^2 = 1.6 x 10^-14 then, (0.025 + x) ( x^2) = 1.6 x 10^-14. The solution however, says that OH- should be set up as 2x instead of x, giving 4x^2, not x^2. I am wondering why would OH- be set up as 2x?

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[Dgeorg6]

Not 2012 destroyer I'm assuming?

 

[ahcten]

Balance reaction: Fe(OH)2 --> Fe2+ + 2OH-
Molar concentration for Fe2+ is x and 2OH- is 2x
Ksp = [Fe2+][OH-]^2
1.6 x 10^-14 = (0.025 + x) (2x)^2