Video Transcript
Consider the following reaction:
CdSO4, aqueous, plus K2S, aqueous, react to produce CdS, solid, plus K2SO4,
aqueous. By which of the following methods
are the reaction products most easily separated? (A) Crystallization method, (B)
distillation method, (C) filtration method, (D) titration method, or (E)
volatilization method.
The reaction begins with two
aqueous compounds: cadmium sulfate and potassium sulfide. When these aqueous solutions are
combined, they produce potassium sulfate, a compound soluble in water, and cadmium
sulfide, a compound insoluble in water. Potassium sulfate, being soluble,
remains dissolved in the solution, while cadmium sulfide, being insoluble, forms a
precipitate. So, the end product of this
reaction is an insoluble solid and a liquid.
Now, what is the best method of
separating a liquid from a solid? Filtration and crystallization are
the only methods listed that traditionally separate a solid and a liquid. Thus, we can eliminate answer
choices (B), (D), and (E).
Filtration involves pouring the
mixture through a piece of filter paper to separate an insoluble solid from a
liquid. The water and dissolved potassium
sulfate will pass through the filter paper, while the solid cadmium sulfide will
remain on the filter paper.
Crystallization, on the other hand,
involves heating the water off, which would leave both the cadmium sulfide and the
potassium sulfate in the test tube, as neither of them will evaporate. Crystallization is used to separate
a liquid from a soluble solid, whereas we have a liquid and an insoluble solid.
Thus, of the methods given, the one
which will most easily separate the reaction products is (C), filtration method.
