2.2.2 Where an accurate volume is required

For more accurate work, volumetric glassware is used, these include pipettes, burettes and volumetric flasks. A pipette is shown in Figure 6.

Figure 6 A volumetric pipette

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Photograph of a volumetric pipette.

Figure 6 A volumetric pipette

Volumetric glassware is calibrated with graduation lines; there may be a scale, or just one line indicating a specific volume. Either way, the key point is measurements must always be read from the lowest point of the meniscus (the concave curvature on top of an aqueous solution), and shown in Figure 7.

Figure 7 Reading the level of a meniscus

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This is a close-up image on a test tube containing liquid. The bottom of the meniscus is labelled with an arrow, and another arrow indicates the appropriate measurement reading level in line with the bottom of the meniscus.

Figure 7 Reading the level of a meniscus

So having had a glimpse inside the laboratory, in the next section you will return to the problem posed at the start of this session, how do chemists quantify amounts of atoms and molecules?