http://www.ck12.org Chapter 3. Measurement
- Which of the following is the larger amount: 2.35× 102 L or 3.46× 105 mL?
- List two SI units that would be appropriate for measuring each of the following quantities: volume, weight,
and length.
Introduction
In the last lesson, we studied the concept of measurement and how numbers are used to express various physical
quantities. We studied scale and magnitude and investigated how to use scientific notation and SI units to report
numbers in an efficient and consistent manner. However, we have not yet studied how measurement takes place.
There are many different measurements we make in our investigations of the chemical world. Measurements such
as distance, volume, and mass are important values that are frequently used to describe the characteristics and
behavior of chemical species. To make measurements, we use instruments labeled with a known scale. However, it
is impossible for measurements to be exact. In this lesson, we are going to study how measurements are made as
well as the error and uncertainty involved in measurements.
Uncertainty
FIGURE 3.3
Figure3.3 shows a graduated cylinder, which is an instrument that is used to measure volume. The graduated
cylinder gets its name because of the gradation or scaled lines drawn on its side. These serve as reference points that
correspond to known volumes. When we make a measurement using a graduated cylinder, we look at themeniscus,
or curved surface, of the liquid andestimatewhere the bottom of the meniscus is relative to the gradations. All
measurement devices have reference marks of some kind. Can you think of another example of a measurement
device with regular reference marks?
Example 3.9
Make an estimate of the volume that is shown inFigure3.3.
Answer:
We see the bottom of the meniscus is at approximately 52.9 mL. We report this in mL because our cylinder is a 100
mL graduated cylinder, with mL reference marks. There are 9 equally spaced marks between the 50 mL and 60 mL