Fe2+(aq) + 2OH-(aq)
44) (a) pH = 7.0 Ksp = 7.9 x 10-16
[H+] = 10-pH = 10-7.0 = 1 x 10-7 M
Kw = [H+] x [OH-] = 1.00 x 10-14
[OH-] = Kw/[H+] = (1.00 x 10-14)/(1 x 10-7) = 1 x 10-7 M
Fe(OH)2(s) Fe2+(aq) + 2OH-(aq)
[ ]i 0 1 x 10-7
[ ]c +x +x
[ ]e x 1 x 10-7+x
Ksp = [Fe2+] x [OH-]2
7.9 x 10-16 = x · (1 x 10-7 + x)2 ≈ x · (1 x 10-7)2 = 1 x 10-14x
[Fe2+] = 7.9 x 10-2 M
s = 7.9 x 10-2 mol Fe2+/L x 1 mol Fe(OH)2/1 mol Fe2+ = 7.9 x 10-2 M
(b) pH = 10.0
pH + pOH = 14.00
pOH = 14.00 - pH = 14.00 - 10.0 = 4.0
[OH-] = 10-pOH = 10-4.0 = 1 x 10-4 M
Fe(OH)2(s) Fe2+(aq) + 2OH-(aq)
[ ]i 0 1 x 10-4
[ ]c +x +2x
[ ]e x 1 x 10-4+2x
Ksp = [Fe2+] x [OH-]2
7.9 x 10-16 = x · (1 x 10-4 + 2x)2 ≈ x · (1 x 10-4)2
[Fe2+] = 7.9 x 10-8 M
s = 7.9 x 10-8 mol Fe2+/L x 1 mol Fe(OH)2/1 mol Fe2+ = 7.9 x 10-8 M
(c) pH = 12.0
pH + pOH = 14.00
pOH = 14.00 - pH = 14.00 - 12.0 = 2.0
[OH-] = 10-pOH = 10-2.0 = 1 x 10-2 M
Fe(OH)2(s) Fe2+(aq) + 2OH-(aq)
[ ]i 0 1 x 10-2
[ ]c +x +2x
[ ]e x 1 x 10-2+2x
Ksp = [Fe2+] x [OH-]2
7.9 x 10-16 = x · (1 x 10-2 + 2x)2 ≈ x · (1 x 10-2)2
[Fe2+] = 7.9 x 10-12 M
s = 7.9 x 10-12 mol Fe2+/L x 1 mol Fe(OH)2/1 mol Fe2+ = 7.9 x 10-12 M