General Chemistry I with Lab – Chapter 1.2 Measurements Study Notes & Lab Practice Resource

2026/01/15 General Chemistry I with Lab
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1.2 Measurements
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1.2 Measurements




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Learning Objectives

By the end of this section, you will be able to:

Explain the process of measurement.
Identify the three basic parts of a quantity.
Describe the properties and units of length, mass, volume, density, temperature, and time.
Perform calculations involving the relationships between mass, volume, and density.

Measurements provide much of the information that informs our understanding of the behavior of
matter and energy in both the macroscopic and microscopic domains of chemistry. Every
measurement provides three kinds of information: the size or magnitude of the measurement (a
number); a standard of comparison for the measurement (a unit); and an indication of the uncertainty
of the measurement. While the number and unit are explicitly represented when a quantity is written,
the uncertainty is an aspect of the measurement result that is more implicitly represented and will be
discussed later.




Numbers
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scientific notation. (Scientific notation is also known as exponential notation; a review of this topic can
be found here .) For example, the maximum takeoff weight of a Boeing 777-200ER airliner is 298,000
kilograms, which can also be written as 2.98 × 10⁵ kg. The mass of the average mosquito is about
0.0000025 kilograms, which can be written as 2.5 × 10-6 kg.




Units
Units, such as liters, pounds, and centimeters, are standards of comparison for measurements.
Without units, a number can be meaningless, confusing, or possibly life-threatening. Suppose a
doctor prescribes phenobarbital to control a patient’s seizures and states a dosage of “100” without
specifying units. Not only will this be confusing to the medical professional giving the dose, but the
consequences can be dire: 100 mg given three times per day can be effective as an anticonvulsant,
but a single dose of 100 g is more than 10 times the lethal amount.

Most of the international scientific community has agreed to use a standard set of units, allowing for
easier communication of scientific data regardless of language barriers or differences in national
standards. These units are called the International System of Units or SI Units. SI units are an
updated version of the metric system, composed of the seven fundamental properties listed in the
table below. Units for other properties may be derived from these seven base units.



Table 1.1: Base Units of the SI System


Property
Name of Unit Symbol of Unit
Measured


length meter m


mass kilogram kg


time second s


temperature kelvin K


electric
ampere A
current


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