151
Ionic Interactions
A plot of V o (elect) versus K o (ion) is shown in Figure 4.20. From Figure 4.20, we obtain k =
4800 bars, which can be compared to
k = –(∂lnD/∂P)/[(∂lnD/∂P) – (∂lnD/∂P) 2 ] = 5000 bars
(4.32)
from the Born model. Using the value of k = 4800 bars, we obtain (V o
E – V o
B ) = –3.9 cm 3
mol –1 . Combining this value with V o
B = 18.0 cm 3 mol –1 , we find V o
E = 14.1 cm 3 mol –1 , which
κ × 10
4 (cm
3 mol
–1 bar
–1 )
–140 –120 –100 –80 –60 –40 –20 0
20
40
V° (cm
3
mol
–1
)
–80
–60
–40
–20
0
20
40
25°C
Figure 4.20
Correlation of the molar volumes and compressibilities of electrostriction for metals.
Table 4.4
Hydration Numbers of Solutes at 25°C Determined
from Compressibility Data
Cations
h
Anions
h
Ion Pairs
h
Li+
2.8
F–
5.6
MgSO 4
0
15.3
Na+
3.7
Cl–
2.0
MnSO 4
0
14.2
K+
2.9
Br–
1.2
LaSO 4+
17.3
Rb+
2.9
I–
0.1
LaFeCN 6
0
18.3
Cs+
2.5
OH–
6.4
Ag+
3.4
SO 4
2–
8.6
NH 4+
0.4
CO 3
2–
12.8
Mg 2+
7.8
Zn 2+
5.9
Cu 2+
7.6
Cd 2+
8.5
Ca 2+
6.5
Ba 2+
9.2
La 3+
14.7