Approximately 1.5 10-3 g of iron(II) hydroxide, Fe(OH)2(s) dissolves per liter of water at 18°C. Calculate Ksp for Fe(OH)2(s) at this temperature.

Question

This is what I've done:

1.5x10^-3 g Fe(OH)2/L x 1mol Fe(OH)2/89.863g Fe(OH)2 = 1.669x10^-5 M Fe(OH)2

Fe(OH)2 = Fe + 2OH

Ksp = [Fe][OH]^2

Ksp = [1.669x10^-5][1.669x10^-5]^2

Ksp = 4.6x10^-5

I'm told the answer is wrong. Can anyone please tell me where I'm messing up? Thanks!

Answer 1

Ksp=[Fe}{OH}^2 = n*(2n)^2 where your n is as you stated. The OH is twice the Fe

Answer 2

I don't understand... I thought OH is only raised to the 2nd power? Not multiplied by 2 and then raised to the 2nd power?

So the Ksp should be [Fe][2OH]^2?

Answer 3

Sorry, I understand now... thank you very much for your help!