92168.pdf

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
Wcm
3
(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

area of nitrogen as 16.2 x 10~

20

m

2

.

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/

cm^3 (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

x 10~^20 m^2 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

Volume ofKr adsorbed/cm^3 (s.t.p.) 1 .475 1 .878

If the saturation vapour pressure and molecular area of krypton at

this temperature are 19.0 mmHg and 21 x io~"

20

m

2

, 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: