Video Transcript
When adding a solution from a buret
into an Erlenmeyer flask, why is it important that the flask is swirled?
The experiment described in the
question is a titration experiment. In a titration experiment, a
solution with a known concentration is added to an exact volume of a solution with
an unknown concentration in the presence of an indicator. The solution with the known
concentration is called the titrant, and the solution with the unknown concentration
is called the titrand or analyte.
The apparatus shown could be used
to carry out an acid–base titration. Let’s say the buret contains a
basic solution with a known concentration. Then, the Erlenmeyer flask would
contain a specific volume of acid and phenolphthalein indicator. In an acidic solution,
phenolphthalein indicator is colorless. At a pH of about 8.2,
phenolphthalein turns faint pink. As a solution becomes even more
basic, phenolphthalein turns darker pink.
As we slowly add the base to the
acidic solution in the Erlenmeyer flask, we should continuously swirl the solution
in the flask. As we continue to add the base and
swirl the solution, we will notice that the solution begins to turn pink. However, when we swirl the
solution, the pink color goes away and the solution turns colorless again. This is because all of the base
that was added quickly reacted with the acid and the pH of the solution is still
below seven. But soon after adding more base,
the swirling does not make it go away and the faint pink color persists.
At this point, we have added just
enough base to neutralize all of the acid in the flask. This point is called the
equivalence point, and we should stop our experiment and read the buret to determine
how much base was added. If we continued to add more base,
the solution would turn darker pink as the pH rises. This is because there is no more
acid in the flask to react with the base that has been added. To get the most accurate
measurement of how much base is needed to react with the acid, we need to ensure the
solutions are continuously mixed together well so that they can fully react.
In conclusion, when adding a
solution from a buret into an Erlenmeyer flask, it is important that the flask is
swirled to ensure the solutions are mixed.
