# 2: Units and Dimensional Analysis

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Chemistry, like all sciences, is quantitative. It concerns quantities, things that have amounts and units. Dealing with quantities and relating them to one another is very important in chemistry. In this chapter, we will discuss how we deal with numbers and units, including how they are combined and manipulated.

• 2.1: Scientific Dimensional Analysis
Dimensional analysis (also called factor label method or unit analysis) is used to convert from one set of units to another. This method uses relationships or conversion factors between different sets of units. While the terms are frequently used interchangeably, conversion factors and relationships are different.
• 2.2: The Importance of Units
Measurements require two parts to specify a quantity; a number part and a unit part.  The previous chapter highlighted the number part and how it can properly indicate the significant figures.  This chapter will focus on the unit part and how units correctly indicate the scale of measurements.
• 2.3: The Basic Units of Measurement
Metric prefixes derive from Latin or Greek terms. The prefixes are used to make the units manageable. The SI system is based on multiples of ten. There are seven basic units in the SI system. Five of these units are commonly used in chemistry.
• 2.4: Properties of Matter - Mass, Length, Volume and Temperature
The SI base units specifies certain units for various types of quantities, based on seven fundamental units. We will use most of the fundamental units in chemistry. This section addresses the measurements: mass, length, volume, and temperature
• 2.5: Problem Solving and Unit Conversions
During your studies of chemistry (and physics also), you will note that mathematical equations are used in a number of different applications. Many of these equations have a number of different variables with which you will need to work. Note also that these equations will often require the use of measurements with their units. Algebra skills become very important here!
• 2.6: Solving Multi-step Conversion Problems
Sometimes you will have to perform more than one conversion to obtain the desired unit.
• 2.7: Units Raised to a Power
Conversion factors for area and volume can also be produced by the dimensional analysis method. Remember that if a quantity is raised to a power of 10, both the number and the unit must be raised to the same power of 10.
• 2.8: Density
Density is a physical property found by dividing the mass of an object by its volume. Regardless of the sample size, density is always constant.

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