Page 141 - Gas Adsorption Equilibria

3. Gravimetry 127

2.1.3 Uncertainties or Errors of Measurements
As has been outlined in Chap. 2 uncertainties or errors of measured data
constitute an important part of any kind of experimental work and hence
always should be considered [2.18]. However, for sake of brevity we here
provide the reader only with the formulae allowing one to calculate
uncertainties or mean square deviations (MSD) of the Gibbs excess
mass of an adsorbate which has been measured gravimetrically by
using a two beam balance. This mass can be calculated from eq. (3.14)
combined with eqs. (3.10) and (3.13). By using Gauss’ law of propagation of
uncertainties we have

with

As the thermal equation of state (EOS) of the sorptive gas always can be
written as

with Z = Z(p, T) being the so-called real gas factor or compressibility which
here is assumed to be a well known function of pressure (p) and temperature
(T), we have for the MSD of the gas density

For the MSD of sorbent’s helium volume we have according to (3.13)

with (cp. (3.19))