1. You work in a forensic laboratory and are given an unknown substance, a pale
ID: 1005512 • Letter: 1
Question
1. You work in a forensic laboratory and are given an unknown substance, a pale green crystalline solid, and asked to evaluate its purity and to determine whether it might be identical to a given sample of an illegal drug, a white crystalline solid. Clearly explain what you would do, why you would do it, and how you would interpret your results.
2. You are getting ready to do an experiment and have 1 gram of naphthalene weighed out in a beaker. Someone bumps you from behind and you spill almost all of it in the sand bath. You attempt to carefully scoop it up, but of course some sand gets into it. How can you remove the sand and recover most of the naphthalene in pure form? Explain the options you might consider and what you might decide to do and why.
Explanation / Answer
1. if the sample of the illegal drug reacts with a titrant then that titrant can used with the pale green crystalline solid to determine its purity based on the number of moles of titrant used for the given mass of the sample and the number of moles of the titrant used for the pure drug for the same mass.
2. Two processes could be used for the separation of napthalene from sand:
a) Sublimation :- you can put the mixture in a beaker and cover it with a glass funnel. if sublimation takes place at the current room temperature then no heat is required but if the sublimation temperature is higher than the room temperature then heating would be required. put a spatudal over then glass funnel to collect the sublimate (napthalene) in the pure form.
b) Filtration :- it can be an option if napthalene is dissolved in a non-polar solvent and then filtered through a filter paper. After the filtrate is obtained the solution could be heated to seperate the napthalene form the solution but in this method some sand particles might pass through the filter paper and pure recovery of napthalene may not be possible.
out of the two methods the first method is advisable as it separated the napthalene in its purest form
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