You want to run an experiment using Fe(OH)_3 to confirm the literature data foun

Question

You want to run an experiment using Fe(OH)_3 to confirm the literature data found for this compound. Before you do the experiment you calculate what the literature says you should have at two different temperatures. Show all calculations and solve for the following values with correct units and significant figures. K_sp (25.0 degree C) = 2.790 times 10^-39 K_sp (50.0 degree C) = 4.653 times 10^-38 pH (25.0 degree C) = pH (50.0 degree C) = Delta G (25.0 degree C) = Delta G (50.0 degree C) = Delta S degree = Delta H degree =

Explanation / Answer

Fe(OH)3 <-> Fe+3 + 3OH-

Ksp = [Fe+3][OH-]^3

2.79*10^-39 = (S)(3S)^3

27S^4 = 2.79*10^-39

S = (2.79*10^-39)/27)^1/4)

S = 1.00823*10^-10 M

[OH-] = 3S = 3*10^-10 M

pOH = -log( 3*10^-10 = 9.5228

pH = 14-9.5228

pH = 4.4772

for pH at 50°C

use Ksp at 50°C

Ksp = [Fe+3][OH-]^3

4.653*10^-38 = (S)(3S)^3

27S^4 =4.653*10^-38

S = ((4.653*10^-38)/27)^(1/4)

S = 2.0374*10^-10 M

[OH-] = 3S = 3*2.0374*10^-10 M = 6.11*10^-10

pOH = -log( 6.11*10^-10) = 9.21

pH = 14-9.21 = 4.79

c)

dG = -RT*ln(K)

dG = -8.314*298*ln(2.79*10^-39) = 219945.90 J/mol = 219.94 kJ/mol

d)

dG = -RT*ln(K)

dG = -8.314*(273+50)*ln(4.653*10^-38) = 230840.81 J/mol = 230.84 kJ/mol

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