The law of conservation of mass states that matter cannot be created nor destroyed on Earth. Theoretically, when performing a lab, the mass of the reactants should be the same as the mass of the products. However, lab error may occur so that the mass of the reactants and products are not equal. Lab error is defined as any error that is made by the scientist, errors caused by equipment used within the laboratory, errors in the recording of data, calculation errors, and/or errors in the analysis of the data used to derive a conclusion. For example, if the heating of a liquid was involved in your lab, then some mass of the reactant may have been lost due to evaporation. This would cause the mass of your final product to be lower in mass than you would expect. Keeping good notes while performing your lab and calibrating equipment can help reduce lab error within an experiment.