The law of definite proportion states that different samples of a pure compound always contain the same elements in the same proportions by mass (Law, 2005). For example, sodium chloride always contains 39.3% sodium and 60.7% chlorine by mass. In this experiment, a sample of potassium chlorate was thermally decomposed to determine the mass percent of oxygen in the compound.
A crucible containing 0.1g MnO2 catalyst was weighed, and 20g KClO3 was added, and the crucible and contents reweighed. A thermometer was placed in the crucible, and the crucible heated with a Bunsen burner (Manganese, 2005; Potassium, 2005). The crucible was removed from the Bunsen burner as soon as the KClO3 had decomposed to KCl. The thermometer was removed and the crucible and its contents reweighed.
a) Mass of crucible with manganese(IV) dioxide =53.300g
b) Mass of crucible after potassium chlorate was
c) Mass of crucible after heating =61.94g
d) Mass of potassium chloride = mass of crucible before heating - mass of crucible after heating
e) Mass of oxygen in sample of potassium chlorate =
Mass of potassium chlorate - mass of potassium
chloride = 20 - 8.64 =11.36g
f) Mass percent of oxygen in potassium chlorate =11.36 %
20.00
2. Calculation of theoretical mass percent of oxygen in KClO3
theoretical mass percent of oxygen = mass of 3 oxygen atoms
mass of KClO3
39.0983 + 35.4537 + (15.994 x 3)
3. Calculating the percent error in the experiment using the
experimental and theoretical values of
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