What is the molar solubility of Fe(OH)3(s) in a solution that is buffered at pH 2.75? The Ksp of Fe(OH)3 is 6.3 × 10-38.
3.543x10^-4
very little
To determine the molar solubility of Fe(OH)3 in a solution buffered at pH 2.75, we need to consider the pH and the given solubility product constant (Ksp) value.
Here's how to approach the problem:
1. pH and solubility: The solubility of Fe(OH)3 is affected by pH because it acts as an amphiprotic substance, meaning it can behave as both an acid and a base. At low pH, it tends to dissolve more readily due to the acidic conditions.
2. Balanced Equation: Write the balanced equation for the dissolution of Fe(OH)3 in water:
Fe(OH)3(s) ⇌ Fe3+(aq) + 3OH-(aq)
3. Ksp Expression: The solubility product constant (Ksp) expression for Fe(OH)3 is:
Ksp = [Fe3+][OH-]^3
4. Relationship between pH and [H+] or [OH-]: At pH 2.75, you can calculate the concentration of hydroxide ions ([OH-]) using the equation:
pOH = 14 - pH
[OH-] = 10^(-pOH)
5. Substitute into Ksp expression: Substitute the concentration of OH- from step 4 into the Ksp expression from step 3. Let's denote the molar solubility of Fe(OH)3 as 's':
Ksp = (s)(10^(-pOH))^3
6. Solve for s: Rearrange the equation from step 5 to solve for the molar solubility 's':
s = (Ksp / (10^(-pOH))^3)^0.333
7. Calculate s: Plug in the given Ksp value (6.3 × 10^(-38)) and the pH value (2.75) into the equation from step 6 to calculate the molar solubility.
By following these steps, you should be able to determine the molar solubility of Fe(OH)3 in the buffered solution at pH 2.75.