Final answer:
Fe(OH)₂ will precipitate when the concentration of Fe²+ exceeds a certain value. The solubility product expression and the pH of the buffer solution can be used to calculate this concentration.
Step-by-step explanation:
The precipitation of Fe(OH)₂ can occur when the concentration of Fe²+ exceeds the solubility product constant (Ksp) for Fe(OH)₂. The solubility product expression for Fe(OH)₂ is [Fe²+][OH-]². Given that Ksp = 4.87 × 10-17, we can set up the following equation:
[Fe²+][OH-]² = 4.87 × 10-17
Since the pH of the buffer solution is 9.49, we can calculate the concentration of hydroxide ions (OH-) using the equation 10^(-pOH). Substituting the pH value, we get:
[OH-] = 10^(-9.49)
Now, we can substitute the calculated value of [OH-] into the solubility product expression to find the maximum concentration of Fe²+:
[Fe²+] = 4.87 × 10-17 / [OH-]²
Calculating this expression will give us the concentration of Fe²+ above which Fe(OH)₂ will precipitate.