Illustrated Guide to Home Chemistry Experiments

34 DIY Science: Illustrated Guide to Home Chemistry Experiments

burette clamp is most often used to support a burette, but is

also useful for holding any slender glassware.

A tripod stand provides a stable elevated surface upon which

to heat flasks and beakers, typically over an alcohol lamp. A

tripod stand is more accident-prone than a ring stand because

the vessel isn’t clamped, but tripod stands are inexpensive and

suitable for heating small containers if you’re careful not to

knock them over.

PPETTERSI

A pipetter is a device used to fill pipettes and then deliver the

liquid in a controlled fashion. A bulb pipetter is the simplest

and cheapest type. It’s a plain rubber bulb, similar to the ones

used on eyedroppers, but sized to the capacity of the pipette.

Ordinarily, you use the suction of the bulb to fill the pipette

above the zero mark, and then quickly remove the bulb and

use your finger to control the flow. Better bulb pipetters have

multiple valves. You squeeze one place on the bulb to fill the

pipette, another place to deliver the solution in a controlled

fashion, and still a third place to dump the contents quickly.

A pipette pump, shown in Figure 3-25, is a plastic device that

friction-fits the top of the pipette. A thumb wheel allows you to

draw in liquid, which can then be released in controlled fashion.

You’ll want at least one pipetter that’s appropriate in size for

each size of pipette you have. Some pipetters can be used with

more than one size of pipette.

PASURI MH E nG TOOLS

An aqueous solution can range from pH 0 (strongly acid)

through pH 7 (neutral) to pH 14 (strongly basic). It’s often

important to have some idea of the pH of a solution. Sometimes,

all you need to know is whether the solution is acidic or basic.

Other times, you need to know the pH with some precision.

For a quick and dirty determination of pH, indicator papers

are the traditional choice. Litmus paper is so familiar even to

nonchemists that the phrase “litmus test” has become part of

the vernacular. Litmus paper turns red at pH 4.5 and below, and

blue at pH 8.3 and above. When wet with a solution that has a

pH between 4.5 and 8.3, litmus paper turns an intermediate

purplish color. Even in laboratories that have expensive, precise

electronic pH meters available, litmus paper is still used when

all that’s needed is a quick test for acidity or alkalinity. Every lab

needs at least two vials of litmus paper, one red and one blue.

When you need a more precise indication of pH, you can use

pHydrion paper or universal indicator paper, which use a

combination of indicator dyes to provide a wide range of color

changes at different pH levels. Such papers are available in

broad- and narrow-range forms. Broad-range papers test all or

most of the range of pH values from 0 to 14, but with accuracy

limited to ±0.5 pH. Narrow-range papers are available in various

FIGURE 3-23: A ring with clay triangle

FIGURE 3-24: A utility clamp supporting an Erlenmeyer flask

dELToN’T m yoUR CLAmpS

Many clamps have plastic or cork insulation on

their jaws. If you use a clamp to secure a vessel that’s

being heated, make sure that the insulation can take

the heat. In general, plastic or cork insulation is usable

if the temperature won’t exceed that of boiling water.

For procedures that use higher temperatures, such as

destructive distillations, use either solid metal clamps

or those with insulation designed to stand up to

those temperatures.