Units, Measurements, and Conversion Factors

Introduction

In general chemistry, understanding units, measurements, and conversion factors is essential for solving quantitative problems. This section covers the basic units used in chemistry, common prefixes, and how to convert between different units using conversion factors.

Units of Measurement

Measurements in chemistry are expressed using standardized units. The International System of Units (SI) is the most widely used system in science.

• Length: The SI unit is the meter (m).

• Mass: The SI unit is the kilogram (kg).

• Time: The SI unit is the second (s).

• Amount of substance: The SI unit is the mole (mol).

• Temperature: The SI unit is the kelvin (K).

Common Prefixes and Their Meanings

Prefixes are used to indicate multiples or fractions of units. Some common prefixes include:

• kilo- (k): (1,000 times the base unit)

• centi- (c): (1/100 of the base unit)

• milli- (m): (1/1,000 of the base unit)

• micro- (\mu): (1/1,000,000 of the base unit)

Conversion Factors

Conversion factors are ratios used to express the same quantity in different units. They are essential for converting between units in calculations.

• Definition: A conversion factor is a fraction in which the numerator and denominator are equal quantities expressed in different units.

• Example: , so the conversion factors are or .

Examples of Common Conversions

• Length:

• Mass:

• Volume:

• Distance around the Earth (circumference):

Sample Conversion Problem

To convert 2.5 kilometers to meters:

• Set up the conversion:

Table: Common Conversion Factors

Significant Figures and Scientific Notation

When performing conversions, it is important to keep track of significant figures and use scientific notation for very large or small numbers.

• Scientific Notation: A way to express numbers as a product of a number between 1 and 10 and a power of 10. For example, .

• Significant Figures: The digits in a measurement that are known with certainty plus one estimated digit.

Summary

• Always use the correct units in calculations.

• Apply conversion factors to change from one unit to another.

• Keep track of significant figures and use scientific notation as needed.

Additional info: Some context and examples were inferred to provide a complete and self-contained study guide, as the original material was fragmented and partially illegible.