Transcript Document

Lesson 4
Calculating
Solubility
1.
Calculate the solubility @ 25oC for BaCrO4 in units of g/L.
⇌
BaCrO4(s)
s
from page 5
Ba2+
s
+
CrO42s
Ksp
=
[Ba2+][CrO42-]
Ksp
=
s2
=
s2
1.2 x 10-10
s
=
1.1 x 10-5 M
note that solubility units are M!
1.1 x 10-5 mole
L
x
253.3 g
1 mole
=
0.0028 g/L
2.
Calculate the solubility @ 25oC for Cu(IO3)2 in units of g/L.
⇌
Cu(IO3)2(s)
Cu2+
s
2.584 x 10-3 moles
L
+
s
2s
Ksp
=
[Cu2+][IO3-]2
Ksp
=
[s][2s]2
Ksp
=
4s3
6.9 x 10-8
=
4s3
s
=
2.6 x 10-3 M
x
413.3 g
1 mole
=
2IO3-
1.1 g/L
note sig figs are 2 like the Ksp!
3.
Calculate the molar solubility @ 25oC for Fe(OH)3. Calculate the mass
required to prepare 2.0 L of the above saturated solution.
⇌
Fe(OH)3
s
=
[Fe3+][OH-]3
Ksp
=
[s][3s]3
=
27s4
=
9.906 x 10-11 M
s
x
3OH3s
+
Ksp
2.6 x 10-39
2.0 L
Fe3+
s
9.906 x 10-11 mole
L
x 106.8 g
1 mole
=
2.1 x 10-8 g
The size of the Ksp is related to the solubility of the ionic compound. For salts that
are comparable (AB versus AB), the larger the Ksp of the salt, the greater is its
solubility.
4.
Indicate the solid with the greatest solubility.
PbSO4
low
ZnS
low
AgCl
low
BeS
high
start on page 4
One of These Things is not like the Other
5.
Indicate the solid with the least solubility.
PbSO4
low
1.8 x 10-8
ZnS
low
2.0 x 10-25
AgCl
low
1.8 x 10-10
BeS
high
start on page 4
use page 5 if required
The lowest ksp is the lowest solubility
6.
A solution of AgNO3 is slowly added to a mixture containing 0.10 M I-, Cl-,
Br-, and IO3-. The precipitate, which forms first, is
AgI
low
8.5 x 10-17
AgCl
low
1.8 x 10-10
AgBr
low
5.4 x 10-13
AgIO3
low
3.2 x 10-8
lowest ksp – 1st ppt to form
7.
A few drops of AgNO3 is added to four beakers containing 0.10 M I-, Cl-,
Br-, and IO3-. A precipitate forms in three of the solutions. The solution
that does not form a precipitate is?
AgI
low
8.5 x 10-17
AgCl
low
1.8 x 10-10
AgBr
low
5.4 x 10-13
AgIO3
low
3.2 x 10-8
highest ksp – last ppt to form
Sodium acetate sculptures