Chapter 3: Equipping a Home Chemistry Laboratory 17DEROUSAnG ASSUMPTIOnS
In order to make Figure 3-5 more visually appealing, we
filled the flasks with attractively colored solutions. The 50
mL flask contains tap water with a few drops of green food
coloring. The 125 mL flask contains tap water with a few
drops of red food coloring. The 250 mL flask contains tap
water with a few drops of yellow food coloring. The 500
mL flask contains tap water with... several grams of a
toxic copper compound.
Or does it? We may have used blue food coloring in the
500 mL flask and a toxic chromium compound in the 50
mL flask. The point is that we can’t tell just by looking, and
neither can you.
Never judge the contents of a flask or other container by
visual appearance alone.z
FIGURE 3-5: Erlenmeyer flasks in various sizes FIGURE 3-6: A 250 mL flat-bottom Florence flask
receivers for a distillation apparatus, and so on. In addition to the
volumetric flasks detailed later in this chapter, there are three
main types of general-purpose laboratory flasks.
ERLENmEyER fLASkS
An Erlenmeyer flask, shown in Figure 3-5, has a wide, flat base and a
conical cross section, which allows it to sit on the lab bench without
risk of tipping. We frequently use an Erlenmeyer flask, also called a
conical flask, for a task that requires a vessel larger than a test tube.
A well-equipped home chemistry lab should have Erlenmeyer
flasks in various sizes. You’ll need at least one 500 mL and two
250 mL Erlenmeyer flasks, but it’s useful to have several 125 mL
or 250 mL flasks. Like beakers, Erlenmeyer flasks can often be
purchased in boxes of six or twelve at a significant discount, and
are available in assortments of various sizes at a discount.
fLoRENCE (BoILING) fLASkS
A Florence flask, also called a boiling flask, is specifically
designed for vigorous boiling. Florence flasks are more robust
than Erlenmeyer flasks, and are less likely to break from physical
or thermal shock. A Florence flask is a good reaction vessel for
distillations, refluxing, and similar operations. There are two
varieties of Florence flask. A flat-bottom Florence flask, shown in
Figure 3-6, has a small flat area on the bottom of the flask, which
means that it can sit stable on a flat surface and can be heated on
a wire mesh. A round-bottom Florence flask must be supported
by a clamp at all times. In most home chem labs, an Erlenmeyer
flask can be used instead of a Florence flask for occasional
distillations and similar operations. If you plan to do frequent
distillations, particularly on a larger scale or with high-boiling
liquids, have at least one Florence flask on hand. The 250 mL and
500 mL sizes are the most useful.fILTERING fLASkS
A filtering flask, shown in Figure 3-7, looks like an Erlenmeyer
flask with a side arm. In use, tubing connects a vacuum source
to the side arm, establishing a vacuum in the flask. A formal
laboratory provides connections to a central vacuum pump. In a
home laboratory, the vacuum source is usually a hand vacuum
pump or an aspirator connected to a water faucet. The suction