386
Solubility Product and Precipitation
23. When a metal ion precipitates from an unbuffered solution on saturation with
H 2 S, the acidity of the solution increases as the metal removes the S
2 ~. This in
turn increases the solubility of the metal sulfide. What will be the concentration of each of the following metals remaining after saturation of 0.100 M
aqueous solutions with H 2 S?
(a) Cu
2+
(b) Cd
2+
(c) Zn
2+
24. A 0.0500 M ZnCl 2 solution is buffered with 2.00 moles of NaC 2 H 3 O 2 and 1.00
mole of HC 2 H 3 O 2 per liter. What will be the Zn
2+ concentration remaining after
saturation with H 2 S?
25. A solution saturated with CO 2 at 1 atm and 25.0°C has a concentration of about
0.0340 M.
(a) Write an equilibrium expression, in terms of H
+ and CO|~, that could be
usefully applied to the separation of metal ions as carbonates by saturation
with CO 2 .
(b) At what pH must a solution be adjusted so as not to precipitate BaC0 3
from a 0.0200 M Ba(NO 3 ) 2 solution on saturation with CO 2 ?
(c) What would be the concentration of Pb
2+ remaining in a solution adjusted
to the pH in (b)?
(d) Why can't saturation with CO 2 be applied in a practical way to the separation of metal ions in the same way that saturation with H 2 S is?
26. Which will precipitate first when solid Na 2 S is slowly added to a 0.0100 M
MnSO 4 solution: MnS or Mn(OH) 2 ?
27. Calculate the solubility in water of (a) PbS and (b) T1 2 S. (Do not neglect
hydrolysis of the sulfide ion.)
PROBLEMS B
28. The following solubilities in water have been determined by experiment. From
these experimental data, calculate the solubility products for the solids involved. The solubilities are given in grams/100 ml of solution.
(a) CaCO 3 , 6.93 x lO'
4
(e) CaF 2 , 1.47 x 10"
3
(b) AgCN, 1.50 x 10?
(f) Ce(IO 3 ) 3 , 0.123
(c) PbI 2 , 5.41 x 102
(g) MgNH 4 PO 4 , 8.66 x 10'
3
(d) Ag 2 S, 6.11 x 10-'
6
(h) Hg 2 Br 2 , 1.36 x 10~
6
29. Which of the following solids will dissolve readily in an excess of 1.00 M HC1?
(a) CaF 2
(e) Cd(OH) 2
(b) AgBr
(f) BaSO 4
(c) MgC0 3
(g) MgC 2 0 4
(d) BaCrO 4
30. In each of the following cases show whether a precipitate will form under the
given conditions.
(a) 1.00 g of Sr(NO 3 ) 2 is added to 1 liter of 0.00100 M K 2 CrO 4
(b) 1.00 ml of 0.0100 M Pb(NO 3 ) 2 is added to 1 liter of 0.0100 M H 2 SO 4
Solubility Product and Precipitation
23. When a metal ion precipitates from an unbuffered solution on saturation with
H 2 S, the acidity of the solution increases as the metal removes the S
2 ~. This in
turn increases the solubility of the metal sulfide. What will be the concentration of each of the following metals remaining after saturation of 0.100 M
aqueous solutions with H 2 S?
(a) Cu
2+
(b) Cd
2+
(c) Zn
2+
24. A 0.0500 M ZnCl 2 solution is buffered with 2.00 moles of NaC 2 H 3 O 2 and 1.00
mole of HC 2 H 3 O 2 per liter. What will be the Zn
2+ concentration remaining after
saturation with H 2 S?
25. A solution saturated with CO 2 at 1 atm and 25.0°C has a concentration of about
0.0340 M.
(a) Write an equilibrium expression, in terms of H
+ and CO|~, that could be
usefully applied to the separation of metal ions as carbonates by saturation
with CO 2 .
(b) At what pH must a solution be adjusted so as not to precipitate BaC0 3
from a 0.0200 M Ba(NO 3 ) 2 solution on saturation with CO 2 ?
(c) What would be the concentration of Pb
2+ remaining in a solution adjusted
to the pH in (b)?
(d) Why can't saturation with CO 2 be applied in a practical way to the separation of metal ions in the same way that saturation with H 2 S is?
26. Which will precipitate first when solid Na 2 S is slowly added to a 0.0100 M
MnSO 4 solution: MnS or Mn(OH) 2 ?
27. Calculate the solubility in water of (a) PbS and (b) T1 2 S. (Do not neglect
hydrolysis of the sulfide ion.)
PROBLEMS B
28. The following solubilities in water have been determined by experiment. From
these experimental data, calculate the solubility products for the solids involved. The solubilities are given in grams/100 ml of solution.
(a) CaCO 3 , 6.93 x lO'
4
(e) CaF 2 , 1.47 x 10"
3
(b) AgCN, 1.50 x 10?
(f) Ce(IO 3 ) 3 , 0.123
(c) PbI 2 , 5.41 x 102
(g) MgNH 4 PO 4 , 8.66 x 10'
3
(d) Ag 2 S, 6.11 x 10-'
6
(h) Hg 2 Br 2 , 1.36 x 10~
6
29. Which of the following solids will dissolve readily in an excess of 1.00 M HC1?
(a) CaF 2
(e) Cd(OH) 2
(b) AgBr
(f) BaSO 4
(c) MgC0 3
(g) MgC 2 0 4
(d) BaCrO 4
30. In each of the following cases show whether a precipitate will form under the
given conditions.
(a) 1.00 g of Sr(NO 3 ) 2 is added to 1 liter of 0.00100 M K 2 CrO 4
(b) 1.00 ml of 0.0100 M Pb(NO 3 ) 2 is added to 1 liter of 0.0100 M H 2 SO 4