A student's correctly calculated value for the percent recovery of the purified unknown solid in a recrystallization experiment was 102%. Assume that the student performed all steps of the procedure correctly
a) comment of the validity of this result; include reasons
b) suggest possible explanation for such a result
Either the student witnessed a miracle, or a measurement error occurred. I would suspect the latter.
Another possibility is that the measurements were ok but the product contained some of the impurity or some of the solvent.
a) The validity of a percent recovery value exceeding 100% in a recrystallization experiment is questionable. In theory, a percent recovery value should not exceed 100%, as it represents the fraction of the original unknown solid that was successfully recovered after the recrystallization process. A value greater than 100% suggests that more solid was recovered than was initially present, which is not feasible. This result raises doubts about the accuracy of the calculation or the analysis performed.
b) Possible explanations for a percent recovery exceeding 100% could include errors in measurement or calculation, contamination of the recovered solid with impurities, incomplete evaporation of solvent resulting in additional solid recovery, or the presence of multiple compounds with similar properties in the original mixture. It is essential to thoroughly investigate the experimental procedure, starting from the initial weighing of the unknown solid, to identify any potential sources of error that may have led to this unexpected result.