86
FIGURE 7-1
Volumetric flask filled
to the mark with a liquid.
PROBLEM:
A clean dry 10-ml graduated cylinder weighs 37.6 g empty; it weighs 53.2 g when
filled to the 7.4 ml mark with an unknown liquid. Calculate the density of the
liquid.
SOLUTION:
The weight of the liquid is 53.2 g - 37.6 g = 15.6 g.
The volume of the liquid is 7.4 ml.
15 6 g
The density of the liquid =
—, = 2.1 —-.
7.4 ml
ml
A more accurate value, using the same method, involves a volumetric flask
as the vessel and an analytical balance for the weighings. The volumetric flask
has a narrow neck that makes accurate measurement easy; liquid is added until
the bottom of the curved liquid surface (the meniscus) appears to just touch the
mark that is etched on the neck (Figure 7-1).
PROBLEM:
A clean dry volumetric flask, known to contain exactly 10.000 ml when it is
properly filled to the mark, weighs 12.754 g when empty. When filled to the mark
with a liquid at 23°C, it weighs 33.671 g. Calculate the density of the liquid.
SOLUTION:
Density =
10.000 ml
= 2.092
at 23°C
ml