CEM 262
Recitation Exercise #7
Solubility Product Calculations
1. (a) The concentration of Al3+ in a sample is determined by gravimetric analysis. In order to
precipitate the Al3+ out as Al(OH)3, the pH of the solution is increased from pH 1.0 to pH
10.0 by addition of urea and heating. How many milligrams of Al3+ remain dissolved in the
solution after the Al(OH)3 has precipitated out?
Possibly useful information:
Solution temperature is 25 °C.
Solution volume is 100 mL.
Ksp of Al(OH)3 is 3 x 10-34 at 25 °C.
Assume that the ionic strength of the solution is very low.
Final pH = 10.0
FW of Al(OH)3 is 77.10 g/mol.
Atomic weight of Al is 26.98 g/mol.
Mass of Al(OH)3 precipitated is 0.567 g.
(b) Explain why you would add urea to the solution to raise the pH, instead of adding
some concentrated NaOH to raise the pH to 10 immediately.
2. How many grams of Ag2CrO4 can be dissolved in a 500 mL of a 0.050 M NaNO3 solution?
Possibly useful information:
The temperature is 25 °C.
Ksp of Ag2CrO4 is 1.2 x 10-12 at 25 °C.
FW of Ag2CrO4 is 331.730 g/mol.
FW of NaNO3 is 84.99 g/mol.
3. Thallium (I) nitrate (TlNO3) is added to a 0.10 M KCl solution until the Tl+ concentration is
0.0020 M. No precipitate forms. Is this solution unsaturated, saturated, or supersaturated
with TlCl?
Justify your answer with calculations. Assume that the volume of the solution is unchanged
by the addition of TlNO3. Important: Is it reasonable to consider this an ideal solution?
Possibly useful information:
Solution temperature is 25 °C.
Solution volume is 350 mL.
Ksp of TlCl is 1.8 x 10-4 at 25 °C.
2
0.51 Z 2 µ
− log γ x = X
1 + (α X µ / 305)
1
2
µ = ([A]Z A2 + [B]Z B2 + [C]Z C2 + )
3
[H 3O + ] =
K a 2CNaHA + K w
1 + (CNaHA / K a1 )