4. The experimental result did not match the theoretical value: there was an experimental error of 45 %. This is a large error, and may not have been due to experimental error. The KClO3 may have had water molecules attached, and these would have constituted part of the original 20g weighed out. Therefore, as the mixture was heated with catalyst, the water would have evaporated as the oxygen molecules were given off, adding to the reduction in weight of the residual KCl. This would have given a disproportionately high value for the apparent oxygen released from the compound. This would give an erroneously high value for the mass percent of oxygen in the compound. Other contaminants may have been present in the crucible which may have contributed to the error.
Law of definite proportions. 92005). Retrieved July 6, 2005 from: