Iron(II) hydroxide has limited solubility in water (Ksp for Fe(OH)3 is 2.79 x 10

Question

Iron(II) hydroxide has limited solubility in water (Ksp for Fe(OH)3 is 2.79 x 10-39). Fe(OH)3 (s) Fe3+ (aq) + 3 OH- (aq) Consider combining 7.47 x 10-12 moles of Fe(NO3)3 and 7.20 x 10-10 moles of NaOH in enough water to make 1.00 L of solution. What is the value of the ion product constant, Qsp and will a precipitate of Fe(OH)3 form?

a) Qsp = 5.38 x 10-21 and a precipitate of Fe(OH)3 forms.

b) Qsp = 5.38 x 10-21 and no precipitate of Fe(OH)3 forms.

c) Qsp = 7.52 x 10-38 and a precipitate of Fe(OH)3 forms.

d) Qsp = 7.52 x 10-38 and no precipitate of Fe(OH)3 forms.

e) Qsp = 2.79 x 10-39 and the solubility limit of Fe(OH)3 in water has just been met (a saturated solution is present).

Can you explain how you calcualted your answer? thanks

Explanation / Answer

Fe(OH)3 ------> Fe+3 + 3 OH- ; Ksp = 2.79*10^-39
Kip = [Fe+3][3OH-]^3
Kip = (7.47*10^-12)(3*7.2*10^-10)^3
Kip = 7.52 * 10^-38

Kip > Ksp hence Fe(OH)3 precipitaion occurs.

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