Illustrated Guide to Home Chemistry Experiments

Chapter 3: Equipping a Home Chemistry Laboratory 27

FIGURE 3-17: A reaction plate FIGURE 3-18: Beral pipettes

RACTIOE n PLATES
A reaction plate, shown in Figure 3-17, is a flat sheet of glass,
plastic, or porcelain with an array of small wells that typically
contain 0.25 mL to 4 mL each. Reaction plates are available in
many sizes with from half a dozen to 96 or more wells. Reaction
plates are widely used in microchemistry to substitute for test
tubes and other containers, but they are equally useful in a
general chem lab when you need to test one reagent against
many unknowns or many reagents against one unknown. For
example, in one of the experiments in the Forensic Chemistry
chapter, we use Marquis reagent (a presumptive test used by
drug enforcement agents) to test many substances found around
the home. If we performed these tests in standard test tubes,
we’d need a fairly large amount of Marquis reagent (and a lot of
test tubes, all of which we’d have to wash after we completed the
tests). Using a reaction plate instead means that we need only a
few drops of Marquis reagent for each test, and we have only one
item to wash when we complete the tests.

It’s useful to have both white and black reaction plates. White
plates make it easier to see color changes. Black plates make it
easier to see precipitates. Alternatively, a clear plastic or glass
reaction plate serves both purposes, according to the color of the
surface that you rest it on.

Reaction plates are available in deep-well models that have
cylindrical, flat-bottom wells and shallow-well models with
wells with rounded bottoms. Models with a large number of
wells generally have wells of lower capacity, and vice versa.
One of the most useful and common sizes is a 24-well deep-
well model that holds 3 mL per well. At a buck or two each,
these are cheap enough that every home chem lab should

have at least a couple on hand. (Having at least two available

makes it easier to do comparative procedures such as

colorimetric comparisons.)

DOPPERSR AnD DISPOSABLE PIPETTES

Droppers and disposable pipettes (also called Beral pipettes)

are used to transfer or dispense small amounts of liquids in a

controlled fashion. The traditional eyedropper, with its glass

tube and rubber bulb, remains useful for these purposes,

particularly when the liquid in question is an organic solvent or

other liquid that would damage or react with a plastic pipette.

(Of course, that same solvent may damage a plastic reaction

plate, which is an argument for having at least one glass or

porcelain reaction plate available.)

Beral pipettes, shown in Figure 3-18, are single-piece injection-

molded plastic dropper pipettes. Beral pipettes are cheap,

disposable, and have many different uses around the lab.

In addition to their intended use, I have used Beral pipettes

as miniature reaction vessels, miniature filtering funnels,

thistle tubes, and, by cutting their bulb ends at a diagonal, as

disposable miniature chemical scoops to avoid contaminating

our stocks of reagent-grade dry chemicals.

In bags of 100, Beral pipettes sell for five or six cents each,

versus two or three times that much if you buy in small

quantities. Beral pipettes come in various sizes, and are rated

by the amount they contain and the number of drops they

dispense per mL. I prefer the standard 150 mm by 5 mm

models, which contain about 3 mL, dispense 25 drops per

mL, and are graduated in mL.