Post-lab Questions
A student completed the experiment but found that the total amount of material recovered weighed more than the original sample. What is the most likely source of error and how may it be corrected?
Source of Error : During the recovery of NaCl, evaporation should be done until all liquid is eliminated. Failure to evaporate all liquid will result in capturing mass of liquid+sodium chloride, which will be more than the actual mass.
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Correction : Repeat the evaporation and weighing procedure until there is no further change in mass.
Mothballs in a closet gradually disappear over time. What happens to this material?
Sublimation process
A package of freshly picked sweet peas weighed 454g (1 lb.). The peas were freeze dried and the recovered peas weighed 122g. What was lost? What is the percent composition of this volatile component?
Lost component : Volatile Linalool
% of linalool
Mass lost/Initial mass×100
[(454-122)/454]×100
(332/454) ×100 = 73.13 %
In part A., why do students have to put the magnets under the paper, not sticking them directly into the mixture?
Sticking the iron on the magnetic would make it difficult to weigh the amount separated since the iron would remain sticky to the magnet.
Also, the magnet would not be re-used in a similar experiment due to presence of iron filings on its surface.
In part B., a student accidentally let some of the vapor escape the beaker. As a result of this error, will the mass of naphthalene you record be too high, too low, or unaffected? Why?
Mass would be too low
Reason : Naphthalene would escape in gaseous form into the air.
