Video Transcript
A titration is set up as shown in
the diagram. Why is the conical flask placed on
a white tile?
In a titration experiment, a
solution with a known concentration is added to an exact volume of a solution with
an unknown concentration. The setup shown in the diagram
includes the essential equipment used in an acid–base titration experiment. This includes a buret, a clamp, a
retort stand, a conical flask, and a white tile. The contents of the buret depend on
the contents of the conical flask. For example, if the buret contains
a basic solution, then the conical flask contains an acidic solution. The stopcock of the buret can be
used to control the flow of liquid from the buret into the conical flask. Currently, the stopcock is in the
closed position, and no liquid can leave the buret.
During the experiment, just enough
of the basic solution would be added to the conical flask to neutralize the acidic
solution. This point is known as the
equivalence point. Even just one more drop of base can
cause the pH of the solution in the flask to change dramatically at this point. To know when the equivalence point
has been reached, chemists typically add an indicator to the solution in the flask
before starting the experiment. The chosen indicator should change
color very near the equivalence point. In the diagram, the solution in the
conical flask has a faint-pink color. This suggests that phenolphthalein
was the indicator used.
Phenolphthalein turns a faintly
pink color at a pH of about 8.2. If we continued to add more base,
the color of the solution would turn darker pink. At this point, the equivalence
point will have been passed, and too much base will have been added. In order to make the most accurate
measurement of base needed to neutralize the acid, we must observe when the solution
first turns and remains faintly pink. Placing a white tile beneath the
conical flask makes it much easier to observe a color change like this.
In conclusion, the conical flask is
placed on a white tile to make it easier to observe any color changes.
