Decomposition of KClO
Determine the value of the gas constant, R, by measuring the decomposition
of potassium chlorate, KClO
, using a liquid displacement method.
Most gases obey the ideal-gas equation, PV = nRT
quite well under
ordinary conditions, that is, at room temperature and atmospheric pressure. Here P is
pressure, V is volume, n is moles of gas and T is absolute temperature. The gas constant,
R, relates these quantities and is now known to have a value of 0.08206 L.atm/mol.K.
Small deviations from this law are observed, however, because real-gas molecules are fi-
nite in size and exhibit mutual attractive forces. The van der Waals equation,
are constants characteristic of a given gas, takes into account these two
causes for deviation and is applicable over a much wider range of temperatures and
pressures than the ideal-gas equation. The term
in the expression (V -
correction for the finite volume of the molecules; the correction to the pressure by the
takes into account the inter-molecular attractions.
In this experiment you will test the validity of the ideal gas law by determining
the gas constant by the thermal decomposition of potassium chlorate, KClO
evolution of O
from the sample can be measured gravimetrically (mass difference) and
by measuring the volume of evolved gas by displacement of water. A manganese(IV)
, catalyst will be used to speed up the decomposition reaction. The overall
reaction is given by:
) + 3O
Analysis of the results will be performed using both the ideal-gas law and the van
der Waals equation. The experiment will be performed in triplicate to establish the
precision of the measured value.
You will work with mixtures of potassium chlorate and potassium chloride, KCl.
From eq. 2 you can see that KCl(s) is a product of the reaction and, consequently, will not
react. If a sample of the KClO
/KCl mixture is accurately weighed before and after the
oxygen has been driven off, the mass of the evolved oxygen can be obtained by
difference. From this moles of O
can be determined. The oxygen can be collected by
displacing water from a bottle or closed flask, and the volume of gas can be determined
from the volume of water displaced. The measurement of displaced water is performed in