Page 292 - Introduction to Colloid and Surface Chemistry

Problems 281
16. The following data refer to the adsorption of nitrogen on 0.92 g
of a sample of silica gel at 77 K, p being the pressure and V the
volume adsorbed:

p/kPa 3.7 8.5 15.2 23.6 31.5 38.2 46.1 54.8
3
Wcm (s.t.p.) 82 106 124 142 157 173 196 227
Saturated vapour pressure (PQ) = 101.3 kPa.

Plot the adsorption isotherm and use the BET equation to calculate a
specific surface area for the silica gel sample, taking the molecular
2
20
area of nitrogen as 16.2 x 10~ m .
17. The following data refer to the adsorption of /t-butane at 273 K
by a sample of tungsten powder which has a specific surface area (as
determined from nitrogen adsorption measurements at 77 K) of 6.5

Relative pressure (p/po) 0.04 0.10 0.16 0.25 0.30 0.37
Volume of gas adsorbed/
3
cm (s.t.p.) g- 1 0.33 0.46 0.54 0.64 0.70 0.77

Use the BET equation to calculate a molecular area for the adsorbed
butane at monolayer coverage and compare it with the value of 32.1
20 2
x 10~ m estimated from the density of liquid butane.

18. At 90 K a 1.21 g sample of a porous solid showed the following
results for the adsorption of krypton:

Pressure/mmHg 1.110 3.078
3
Volume ofKr adsorbed/cm (s.t.p.) 1 .475 1 .878

If the saturation vapour pressure and molecular area of krypton at
2
this temperature are 19.0 mmHg and 21 x io~" 20 m , respectively,
calculate a specific surface area for the solid.
19. The following results refer to the adsorption of nitrogen on a
graphitised sample of carbon black, and give the ratio of the nitrogen
pressures for temperatures of 90 K and 77 K which are required to
achieve a given amount of adsorption: