Chemistry Reference
In-Depth Information
Taking Measurements in the Chemistry Laboratory
The student using the ruler on the right should record
the length of the ribbon to be 1.11 cm. The first digits
are “exact,” because the length is clearly between 1.1
cm and 1.2 cm. The last digit is an “estimation digit,”
because it involves a judgment.
1.0 cm
2.0 cm
The second measurement should be recorded as 1.95
cm or 1.96 cm. Notice, it is okay to disagree on the
value of the estimation digit, because it involves
estimation. What you can't disagree on is the
number of digits that must be recorded. Always
include one and only one estimation digit.
1.0 cm
2.0 cm
The third ribbon appears to have a length of about
1.31 cm. If the student estimates that the ribbon falls
exactly on the 0.3 cm line, he could use his estimation
digit to say that, by recording the measurement as 1.30
cm. In this way, the estimation digit is still significant.
1.0 cm
2.0 cm
Figure 2-3b
Figure 2-3b gives some examples of how to record measurements prop-
erly. Imagine that a number of students are using this ruler to measure
different strips of magnesium ribbon, such as you may use in the laboratory
this year.
Some students show a lack of concern for accuracy when they take
their measurements in the chemistry lab. For some, it seems more impor-
tant to be quick than to be accurate. The problem with this is that the labo-
ratory activities that your instructor is likely to offer depend upon reasonably
accurate measurements. If your measurements are poor, your results will be
inaccurate, and you miss those “magic” moments when the results of an ex-
periment verify some concept or constant that you have been studying in
your text. To get the most out of your learning experiences, put a great
deal of care into the measurements that you take in the lab.
Try the following practice questions and check your answers at the end
of the chapter before moving on to the next lesson.
Lesson 2-3 Review
1.
The term _______________ refers to how close together a set of
measurements are to each other.
