Ground water intially contains 1.800mg/L of iron as Fe3+. What must the pH be raised to in order to precipitat all but 0.30mg/L of iron. The tempertaure is 25 degrees celcius
Fe(OH)3 ==> Fe^+3 + 3OH^-
Ksp = (Fe^+3)(OH^-)^3
You want (Fe^+3) to be 0.3 mg/L. Change that to moles/L, plug into the Ksp expression, and solve for OH^-, then convert to pH. Post your work if you get stuck.
To determine the required pH to precipitate all but 0.30 mg/L of iron from groundwater, we need to use the solubility product constant (Ksp) for iron(III) hydroxide (Fe(OH)3).
The balanced equation for the reaction of iron(III) ions with hydroxide ions to form iron(III) hydroxide is:
Fe3+ + 3OH- -> Fe(OH)3
We can use the Ksp expression to determine the solubility product constant:
Ksp = [Fe3+][OH-]^3
The solubility of Fe(OH)3 is equal to the concentration of Fe3+ ions in solution since the concentration of OH- ions in the solution is determined by the solution's pH.
At the beginning, we have 1.800 mg/L = 0.0018 g/L of Fe3+. We want to precipitate all but 0.30 mg/L = 0.0003 g/L of iron, so the remaining concentration is 0.0015 g/L.
To find the required pH, we need to first calculate the concentration of hydroxide ions (OH-) that will lead to a solubility of 0.0015 g/L. Then, we can determine the pH from the concentration of OH- ions.
Step 1: Calculate the concentration of OH- ions using the solubility equation and the known solubility product constant for Fe(OH)3:
Ksp = [Fe3+][OH-]^3
0.0015 = (0.0015)[OH-]^3 (since the concentration of Fe3+ equals the concentration of OH- for Fe(OH)3 solubility)
Step 2: Solve the equation for [OH-]:
[OH-]^3 = 0.0015
[OH-] = (0.0015)^(1/3) (take the cube root of both sides)
Step 3: Determine the pH using the concentration of OH- ions:
pOH = -log[OH-]
pOH = -log(0.0015^(1/3))
pOH = -log(0.0015^(1/3))
pOH = -log(0.0015)/3
pOH = -(-2.82) / 3
pOH ≈ 0.94
Step 4: Calculate the pH using the pOH value:
pH = 14 - pOH
pH = 14 - 0.94
pH ≈ 13.06
Therefore, to precipitate all but 0.30 mg/L of iron from the groundwater, the pH must be raised to approximately 13.06 at a temperature of 25 degrees Celsius.