Video Transcript
What is meant by the precipitation
method? (A) It is a type of gravimetric
analysis that is based on the heating of the element or compound and determining its
mass by measuring the amount lost from the original mass of the substance. (B) It is a type of gravimetric
analysis that is based on the precipitation of the analyte in the form of a pure,
sparingly soluble compound with a constant and known chemical structure. (C) It is a type of volumetric
analysis that is based on the precipitation of the analyte in the form of a pure,
sparingly soluble compound with a constant and known chemical structure. (D) It is a type of volumetric
analysis that is based on the precipitation of the analyte in the form of insoluble
crystals.
In this question, we need to
determine which of the following statements best describes the precipitation
method. Let’s begin by clearing some space
to discuss how and why chemists use the precipitation method.
The precipitation method, also
known as precipitation gravimetry, is an analytical technique that uses the
formation and mass of a precipitate to determine the mass of an analyte. First, a chemist carries out a
precipitation reaction, in which two soluble substances in solutions are mixed and
form an insoluble precipitate.
For example, if we wanted to
determine the mass of silver nitrate in a solution, we could react it with a
solution of potassium chloride, because we know that the silver chloride that forms
would be insoluble in water. In this example, silver nitrate is
the analyte and potassium chloride is the precipitating agent. At this point in the experiment,
the silver chloride precipitate needs to be separated from the remaining solution,
which contains the potassium and nitrate ions that are not involved in the
reaction.
The precipitate can be isolated by
pouring the mixture onto a piece of folded filter paper inside a funnel and allowing
the solution to flow through into another container. The precipitate must then be rinsed
and dried to remove any impurities. Drying of the precipitate may be
performed in a drying oven. Or if ashless filter paper has been
used, the filter paper can be burned off in an ignition crucible, leaving a dry and
pure precipitate. Finally, the mass of the
precipitate can be obtained by using an analytical balance.
Now we’re ready to bring the answer
choices back up on the screen and select the correct answer.
We know the precipitation method is
a gravimetric technique focused on finding the mass of an analyte. Therefore, we can eliminate
statements (C) and (D), because they include the term volumetric analysis, which
refers to determining the volume of an analyte.
Next, we see that statement (A)
describes the method of heating a substance and measuring the amount of mass
lost. This technique is called
volatilization gravimetry.
Statement (B) describes using a
precipitation reaction to determine the mass of an analyte, which, as we discussed,
is called precipitation gravimetry. Therefore, answer choice (B) must
be the correct answer.
So what is meant by the
precipitation method? It is a type of gravimetric
analysis that is based on the precipitation of the analyte in the form of a pure,
sparingly soluble compound with a constant and known chemical structure.
