Page 296 - Introduction to Colloid and Surface Chemistry

Problems 285
19
constants for the particles and the dispersion medium are 1.6 x 10~ J
19
and 0.4 x 10~ J, respectively, and the zeta potential is -40 mV.
Using equations (8.7) and (8.10) to calculate V R and V A, respectively,
calculate the total interaction energy between two of these particles
when their shortest distance of approach, H y is 0.5 nm, 2 nm, 5 em,
10 nm and 20 nm.

34. The following results were obtained by particle counting
during the coagulation of a hydrosol at 25°C by excess 1-1
electrolyte:

Time/mm 0 2 4 7 1 2 2 0
3
Particle concentrationlHP cm~ 100 14 8,2 4.6 2.8 1.7

Calculate a 'second-order' rate constant, k 2, and compare it with the
value, &2, calculated on the assumption that coagulation is a
diffusion-controlled process.

35. The flow times in an Ostwald viscometer for solutions of
polystyrene in toluene at 25°C are as follows:

3
Concentration/(g/10Q cm ) 0 0.4 0.8 1.2
Flowtimels 31.7 38.3 45.0 51.9
5 3 1
K and a in the expression, [17] = KM", are 3.7 x 10~ m kg" and
0.62, respectively, for this polymer-solvent system. Assuming a
constant density for the solutions, calculate an average relative
molecular mass for the polystyrene sample. How would this relative
molecular mass be expected to compare with the relative molecular
mass of the same sample of polystyrene in toluene determined from
(a) osmotic pressure and (b) light-scattering measurements?
36. The following viscosities were measured for solutions of
3
cellulose acetate in acetone of concentration 0.5 g/100 cm :
3
10- M r 85 138 204 302
4
V10~ Pas 5.45 6.51 7.73 9.40
The viscosity of acetone at the temperature of these measurements is
4
3.2 x 10~ Pa s. Derive an expression from these data which could be