Illustrated Guide to Home Chemistry Experiments

32 DIY Science: Illustrated Guide to Home Chemistry Experiments

kEE pyoUR BALANCE CLEAN

Never weigh chemicals directly on the balance pan.

Instead, tare (zero out) the balance with a weighing paper,

beaker, or similar container in place, and add the chemical

to the weighing paper or container. Although you can buy

purpose-made weighing papers or weighing boats from

laboratory supply vendors, that’s a needless expense.

Instead, just use a piece of waxed paper about the size of

the balance pan. A roll of waxed paper, a pair of scissors,

and a few minutes is all you need to make a large supply of

weighing papers.

oLAESdI REN’T ALwAyS GoodIES

You may be tempted to buy a traditional triple-beam

(0.1 g) or quadruple-beam (0.01 g or centigram) balance.

Although these mechanical balances have some

advantages over the top-loading electronic balance that

we recommend, they also have a serious drawback. The

damping time of a mechanical balance—the time it takes

to settle down and provide an accurate reading—is much

longer than the damping time of a decent electronic

balance, particularly with the quad-beam models that

provide 0.01 g resolution. Although you can weigh samples

just as accurately with a mechanical balance as with

an electronic balance that has the same resolution, the

process is much more awkward and time-consuming with

the mechanical balance.

On the other hand, a mechanical centigram balance

does have one major advantage. By carefully noting the

exact position of the centigram slider, you can interpolate

the weight of a sample to 0.002 g on most mechanical

centigram balances, and to 0.001 g (1 mg) on some.

FIGURE 3-20: An alcohol lamp

HATSURCESE O
Although modern chemistry sets make a point of using “no
flame,” it’s impossible to imagine a real wet-chemistry laboratory
without heat sources. Heat sources are essential for warming
and boiling solutions, bending and drawing glass tubing, drying
samples, and so on. A well-equipped lab should have several heat
sources, including the following:

Alcohol lamp
An alcohol lamp, shown in Figure 3-20, has been a staple of
home laboratories since there have been home laboratories.
Alcohol lamps are inexpensive, widely available, reliable,
relatively safe to use, and provide a gentle heat that is useful
in a wide variety of laboratory procedures. Even if you have
other heat sources, you’ll want an alcohol lamp for general
heating tasks. I got my alcohol lamp as a part of a glassware
assortment offered by United Nuclear, but you can buy one
from any laboratory supply house.

Gas burner
Formal laboratories invariably have burners fueled by
natural gas, which is impractical for most home chem labs.
Fortunately, there are some good, inexpensive alternatives.
Most laboratory supply houses sell gas microburners
(Figure 3-21) that do not require a connection to a natural gas
supply. Instead, they have a self-contained fuel tank that can
be refilled from standard butane cylinders sold by drugstores
and tobacconists.

One advantage of a gas burner is that it provides a much

hotter, more focused flame than an alcohol lamp. Sometimes,

such as when you are heating a solution in a test tube, this

hotter flame is actually undesirable. Other times, for example

when you are trying to reduce a metal ore with carbon, the

higher temperature of the gas flame may be necessary to

initiate and sustain the reaction. (If you have no gas burner,

you can increase the temperature of an alcohol lamp flame

significantly by using a blowpipe or a piece of glass tubing to

blow air into the flame.)

Another advantage of a gas burner is that most models

produce much more heat than an alcohol lamp. For example,

an alcohol lamp takes a long time to bring 250 mL of a solution

to a boil. A gas burner accomplishes the task much faster.

You may already have a suitable gas burner in your garage

or workshop. Bernz-o-Matic and other companies produce

inexpensive burners that use disposable propane cylinders.