Illustrated Guide to Home Chemistry Experiments

18 DIY Science: Illustrated Guide to Home Chemistry Experiments

FIGURE 3-7: A filtering flask with a Büchner funnel

draws liquid through a Büchner funnel atop the flask, greatly
increasing the speed of filtering. If you have an aspirator or other
source of constant suction, you can also use the filtering flask to
dry the material trapped by the filter paper by continuing to draw air
through the Büchner funnel after all of the liquid has been filtered off.

Filtering flasks are readily available in sizes from 125 mL to
1,000 mL or more. A 250 mL or 500 mL filtering flask is generally
the most useful size for a home chem lab. For most filtering
operations you can get by without a filtering flask, using gravity
filtration with a standard funnel and filter paper, as long as you’re
willing to wait as long as it takes for gravity to do its work. Of
course, depending on what you’re filtering, gravity filtration may
take several minutes or even several hours. In some cases, a very
finely divided precipitate may clog the filter paper, bringing gravity
filtration to a dead stop. If that happens, suction is the only cure.

FnLSUn E
Standard funnels are used to transfer liquids into narrow-mouth
containers. A powder funnel resembles a standard funnel, but
has a shorter, wider stem to allow solid chemicals to flow freely
through the funnel.

Filtering funnels are available in two common varieties. One
resembles a standard funnel, but has vertical ridges or channels

inside the body of the funnel that are designed to keep the filter

paper from adhering to the funnel. A Büchner funnel, shown in

Figure 3-7 atop a filtering flask, is a special type of filtering funnel,

designed to be used with suction to speed up filtration.

A safety funnel, also called a thistle tube, is shown in Figure 3-8.

A safety funnel comprises a long tube with an open bulb on the

top end, which may or may not be stoppered. A safety funnel

is usually inserted in a rubber stopper and used to introduce

additional reagents to a reaction vessel during the reaction.

A separatory funnel (or sep funnel), shown in Figure 3-9, is used

to separate multiple layers of immiscible liquids by draining off

the lower layer or layers through a stopcock. Sep funnels are

commonly used, particularly in organic chemistry experiments,

for extraction and washing.

BTTLESO AnD vIALS

Any chemistry lab needs a variety of bottles and vials to store

and dispense chemicals. Although bottles seem mundane,

some home chemists become fascinated with the great variety

available. More than one home chemist has developed a serious

secondary hobby of collecting bottles, some obsessively. I haven’t

been bitten that badly, but will confess that I do have a collection

of old bottles in various fascinating shapes and unusual

FIGURE 3-9: A separatory funnel

FIGURE 3-8: A safety funnel or thistle tube