Chemistry Reference
In-Depth Information
PROBLEMS
3-1 Two “monodisperse” polystyrenes are mixed in equal quantities by weight.
One polymer has a molecular weight of 39,000 and the other has a molec-
ular weight of 292,000. What is the intrinsic viscosity of the blend in ben-
zene at 25
C? The Mark
Houwink
Sakurada constants for polystyrene/
10
2
5
dL/g and
a
benzene are
K
5
9.18
3
5
0.74.
3-2 The following are data from osmotic pressure measurements on a solution
of a polyester in chloroform at 20
C. The results are in ter
ms
of centi-
meters of solvent. The density of HCCl
3
is 1.48 g cm
2
3
. Find
M
n
:
Concentration (g/dL)
h (cm HCCl
3
)
0.57
2.829
0.28
1.008
0.17
0.521
0.10
0.275
3-3 Consider the following data obtained from a series of osmotic pressure (
)
experiments at 310 K. The solutions consist of poly(vinyl acetate) and tol-
uene. Note that
R
π
8.314 J/mol K and that the molar volume of toluene at
310 K is 106 cm
3
/mol.
5
, kg/m
3
Concentration
c
π/c
, J/kg
2.3
16.9
4.3
17.4
6.3
18.3
10.1
21.5
π/c
against
c
using the above data.
(b) Estimate the concentration range over which the truncated osmotic vir-
ial equation (i.e., ignore
c
2
and all higher order concentration terms) is
valid.
(c) Determine the number average molecular weight (kg/mol) of the poly
(vinyl acetate) sample and the second virial osmotic coefficient (m
3
mol/kg
2
).
(d) Calculate the difference between the chemical potential of toluene in
the solution with the polymer concentration of 10.1 kg/m
3
and that of
pure toluene under the same atmospheric pressure.
(a) Obtain a plot of
3-4 One major factor that determines the osmotic pressure of a polymer
solution (
) is the intermolecular interaction between the solvent and
polymer molecules. Such interaction leads to the observed difference in
the chemical potentials of the solvent in the solution and in its pure form
π
