Volumetric
flask is a piece of laboratory glassware that is used to measure a very
accurate and precise amount of a liquid. It is known as vol flask in short.
It is shaped like a Florence flask with a flatter bottom and long neck. The
long and narrow neck is marked, generally by a circumferential scratch or
etch on the glass, at a very accurate measurement. Usually a single flask
can only be used for a certain measurement, e.g. a 200 ml flask can only be
used to measure 200 ml. The volume marks are usually made by machine, so it
can be more assuredly accurate than hand-made marks.
Volumetric flasks are usually marked as TC or TD. TC means "To Contain",
often marked with a certain temperature at which the volume measurement is
most precise. When filled to the circumferential mark on the neck, the TC
flask will contain the indicated amount of liquid. TD means “To Deliver”,
usually a glassware used to deliver a certain amount of liquid. Volumetric
flasks come with a stopper or cap. The stoppers are made of either plastic
or glass and are used for capping the opening at the top of the neck. When a
glass stopper is used, the opening at top of the neck has an outer tapered
ground glass joint and the glass stopper has a matching tapered inner ground
glass joint surface, but often only of stopper quality.
Uses of Volumetric Flask
Volumetric flasks are used in analytical chemistry to produce accurate
solutions. A volumetric flask is used as a container used to measure the
volume of a liquid with extremely high accuracy. It is considered the most
effective way to measure a specific quantity of a liquid. However it cannot
be used to measure just any volume unlike a graduate cylinder. Each
volumetric flask is designed to measure one particular volume. That's why
they come in a variety of sizes, such as 5 ml, 10 ml, 25 ml, 50 ml, 100 ml,
250 ml, 500 ml, 1000 ml, etc.
The volumetric flask is used in two major ways. In one way a solute of known
mass is placed in the flask and dissolved. The other technique involves
placing an aliquot (sample of precisely known volume) of a solution of known
molarity in the flask, then diluting to the mark with solvent. A volumetric
flask is used either for making solutions or diluting a liquid to the size
of the flask. It almost always involves containing a certain amount of a
liquid. It is achieved by adding the solvent to the flask till it reaches
the neck. You should be careful not to add more than the amount the flask is
supposed to measure. If it is done, the process may need to be repeated. It
can lead to problems, especially when working with expensive chemicals.
Common Features of Volumetric Flasks
- They are generally thick-walled and have a solid finish.
- The figures and marks are clearly legible.
- They are made of high quality Pyrex glass and the glass surface is
not attacked by etching or engraving.
- They are marked with either “TC” or “TD”.
- One type of volumetric flask can be used for the measurement of only
a specific volume of liquid.
