Question

What is the K_sp in terms of the molar solubility s for the substance Fe (OH)₃?

A.s

B.s²

C.2s³

^D. 4s³

Answer 1

Fe(OH)₃ is in equilibrium with Fe³⁺ and OH^- ions in solution. The equilibrium can be written as follows:

Fe(OH)₃ -------->   Fe³⁺    +      3OH^-

Thus, Expression for solubility product constant (Ksp) can be written as follows:

Ksp = [Fe³⁺] [OH^-]³

If 's' the molar solutbility of Fe(OH)₃ then, during equilibrium 's' amount of Fe(OH)₃ will dissovle to give 's' amount of Fe³⁺ and '3s' amount of OH^- ions.

Thus, Ksp can be written as follows:

Ksp = s x (3s)³

Ksp = 27 s ⁴

Therefore, value of Ksp for Fe(OH)₃ in terms of molar solubility s is 27 s ⁴

Thus, the option with correct answer is not given.

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[Note: if given ionic compound is Fe(OH)2, then, as per above explanation, expression for Ksp can be written as follows:

Ksp = s x (2s)2

Ksp = 4s3

Thus, in case of Fe(OH)2 correct answer will be option D. 4s3 ]