If iron(III)acetate is added to be 1 × 10^-10 M in an aqueous solution that is 0.10 M NH₃,what is Q_spand will Fe(OH)₃ precipitate? The K_sp of Fe(OH)₃(s)is 4 × 10^-38 and K_b for NH₃ is 1.8 × 10^-5.

Question

Quizplus · Accepted Answer

First, write out the balanced equation for the reaction between iron(III) acetate and water:

Fe(C2H3O2)3 + 3H2O → Fe(OH)3 + 3C2H4O2

The initial concentration of Fe(C2H3O2)3 is 1 × 10^(-10) M, and the concentration of water is essentially constant and can be ignored. The concentration of C2H4O2 (acetic acid) is 0.10 M.

Next, we need to calculate the concentration of hydroxide ions (OH-) in the solution:

Kb = [Fe(OH)3][OH-]^3 / [Fe(C2H3O2)3]
4 × 10^(-38) = x^3 / (1 × 10^(-10) - x)
x = 2.4 × 10^(-20)

Because Fe(OH)3 is a basic salt, it will react with the acetic acid in the solution to form more hydroxide ions:

Fe(OH)3 + 3C2H4O2 → Fe(C2H3O2)3 + 3H2O

Using an ICE table, we can calculate the new concentration of hydroxide ions:

I: 2.4 × 10^(-20) M
C: -3(2.4 × 10^(-20)) M and +3(0.10 M)
E: 7.08 × 10^(-21) M

Finally, we can calculate the pH of the solution:

pOH = -log(2.4 × 10^(-20)) = 20.62
pH = 14 - pOH =  6.38

Since the pH is greater than 7, the solution is basic and Fe(OH)3 will precipitate. Therefore, the answer is D.

If Iron(III)acetate Is Added to Be 1 × 10-10 M

If Iron(III)acetate Is Added to Be 1 × 10^-10 M