Final answer:
To determine the pH at which a 0.4 M Al3+ solution will begin to show precipitation of Al(OH)3, calculate the concentration of OH- ions required to reach the solubility product (Ksp) of Al(OH)3.
Step-by-step explanation:
To determine the pH at which a 0.4 M Al3+ solution will begin to show precipitation of Al(OH)3, we need to calculate the concentration of OH- ions required to reach the solubility product (Ksp) of Al(OH)3. The Ksp value for Al(OH)3 is given as 2 x 10^-32. We can set up an expression for the solubility product:
Ksp = [Al3+][OH-]^3
Since Al(OH)3 has a 1:3 stoichiometric ratio, the concentration of OH- ions required to reach the Ksp can be calculated by taking the cube root of Ksp: [OH-] = (Ksp)^(1/3) = (2 x 10^-32)^(1/3)
Calculate this value and take the negative logarithm to find the pH at which precipitation of Al(OH)3 will occur.