The solubility of Fe(OH)2 is 2.1 x 10-4 g L-1. What is the Ksp for Fe(OH)2 at 25 °C?

Select one:
a. 5.3 x 10-12
b. 4.3 x 10-8
c. 4.9 x 10-17
d. 5.7 x 10-10

1 Answer
Ernest Z.
May 26, 2018

The closest value is c. #K_text(sp) = 4.9 ×10^"-17"#

Explanation:

Step 1. Calculate the molar solubility

#s = (2.1 × 10^"-4" color(red)(cancel(color(black)("g"))))/"1 L" × "1 mol"/(89.86 color(red)(cancel(color(black)("g"))))= 2.34 × 10^"-6" color(white)(l)"mol/L"#

Step 2. Calculate the solubility product

#color(white)(mmmmml)"Fe(OH)"_2 → "Fe"^"2+" + "2OH"^"-"#
#"I/mol·L"^"-1": color(white)(mmmmmmm)0color(white)(mmmll)0#
#"C/mol·L"^"-1": color(white)(mmmmmm)"+"scolor(white)(mmll)"+2"s#
#"E/mol·L"^"-1": color(white)(mmmmmmll)scolor(white)(mmmll)2s#

#K_text(sp) = ["Fe"^"2+"]["OH"^"-"]^2 = s(2s)^2 = 4s^3 = 4 (2.34 × 10^"-6")^3 = 5.1 × 10^"-17"#

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