Fertilizing the Sea to Combat Global Warming Some scientists have proposed addin

Question

Fertilizing the Sea to Combat Global Warming Some scientists have proposed adding Fe(III) compounds to large expanses of the open ocean to promote the growth of phytoplankton that would in turn remove CO_2 from the atmosphere through photosynthesis. The average pH of open ocean water is 8.1. What is the maximum value of [Fe^3+] in pH 8.1 seawater if the K_sp of Fe(OH)_3 is 1.1 times 10^-36 Number M If you were to predict the solubility (s) of Fe(OH)_3 in seawater using the equation K_sp = (m^Mx^X)S^(m + x) would the prediction be accurate? Yes No, the prediction is higher No, the prediction is lower

Explanation / Answer

Fe(OH)3 (s) <----> Fe3+ (aq) + 3OH- (aq)

Ksp = [Fe3+] [OH-]^3

given pH = 8.1 , pOH = 14-8.1 = 5.9 , [OH-] = 10^ -pOH = 10^ -5.9 = 1.26 x 10^ -6 M

now Ksp = 1.1 x 10^ -36 = [Fe3+] ( 1.26x10^-6)^3

[Fe3+] = 5.5 x 10^ -19 M

b) if we do based on S

[Fe3+] = S , [OH-] = 3S

Ksp = [Fe3+][OH-]^3 = ( S) ( 3S^3) = 27 S^4

1.1 x 10^ -36 = 27S^4

S = 4.5 x 10^ -10 = [Fe3+]

No , prediction is higher

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