Chemistry Reference
In-Depth Information
you were to round off so many measurements in one day, the little incre-
ments would start to add up. For this reason, the supermarket is equipped
with a much more sensitive scale than you are likely to have at home. Both
scales do the jobs that they were designed to do, but they are not created
equal.
As are the instruments that they use, not all students take measure-
ments the same way. Some students take very careful measurements, re-
cording every digit that their instrument allows; others take quicker
measurements, mentally rounding off the numbers that they see. This should
not be the case. If you weigh yourself on a scale at home and it reads 158 lbs.,
there is no harm if you round up to the nearest tens place. You can tell
people that you weigh 160 lbs., and it is not likely to make any kind of
difference, unless you need an accurate weight for a sports team. Chemis-
try, however, is a science that deals with microscopic atoms, and small varia-
tions in mass or volume are often significant. For this reason, every student
should take each measurement the same way. You will want to use each
instrument correctly and record every digit that the instrument allows. Try
to avoid the mental “rounding off” that you might practice when taking
measurements in your daily life.
When you take measurements in your chemistry laboratory, record
every digit that each instrument allows, and include one additional estima-
tion digit. This is very important, as you will see in the next lesson, because
when you perform calculations with these measured values, our answers
can only be as accurate as our least accurate measurement. Before you use
an instrument for a measurement, you should look at it and determine to
what place value it will allow you to measure. Look at the ruler section
shown here in Figure 2-3a.
Upon examination, you should note
that each line or gradation on the ruler
represents a tenth of a centimeter. This
means that you can accurately measure
the length of an object to the tenth of a centimeter. In science, remember,
you are allowed to add one additional estimation digit. This means that
you can add a digit, which estimates how far between lines an object ap-
pears to reach. The place value that you should record to is dictated by the
instrument, not the object that you are measuring, and every student who
uses this ruler should be recording his or her measurements to the hun-
dredth of a centimeter.
1.0 cm
2.0 cm
Figure 2-3a
