One of the key learning objectives for the chemistry 121 lab is for students to learn how to
make
measurements; how to know which equipment to use for what type of measurement and
how to record
the measurement to the correct number of significant figures.
Scientists generally measure liquids using volume measurements and solids using mass
measurements.
This is different than the common types of measurements used in cooking; often solids are
measured
using volumes because of historical tradition and because it seems to work most of the
time. In science,
however, we want to make sure that our measurements are all repeatable by someone other
than
ourselves (science is all about repeatable results!). The volume of a solid, or the space the
solid
occupies, is not useful information if the substance can be compacted or expanded or if the
solid is an
irregular shape that is difficult to measure. Take a cotton ball as an example. The ball is
made up of
solid fibers of cotton grouped together into a ball. If the ball is squeezed in your hand, the
volume is
much less than before you squeezed it. Using volume as a way to define how much cotton
is present is
meaningless. If instead we find the mass of the cotton ball, it stays constant regardless of
what we do to
the shape or volume of the cotton ball and our measurement is repeatable regardless of
who measures.
As we have learned in class, a measurement’s number of significant figures directly relates
to the
uncertainty of the piece of equipment used to make the measurement. Measurements
