Chapter 1: Matter, Energy, and Measurement – GOB Chemistry Study Notes

Introduction to Chemistry: Matter, Energy, and Measurement

Overview

This chapter introduces the foundational concepts of measurement in chemistry, including the metric and SI systems, units, significant figures, and the importance of accuracy and precision. Mastery of these topics is essential for all subsequent work in chemistry.

Units of Measurement

SI Base Units

The International System of Units (SI) is the standard system used in science. Each physical quantity has a specific base unit.

Physical Quantity	Name of Unit	Abbreviation
Mass	Kilogram	kg
Length	Meter	m
Time	Second	s
Temperature	Kelvin	K
Amount of substance	Mole	mol
Electric current	Ampere	A
Luminous intensity	Candela	cd

Metric Prefixes

Prefixes are used to indicate multiples or fractions of base units, making it easier to express very large or small quantities.

Prefix	Abbreviation	Meaning	Example
Giga	G	109	1 gigameter (Gm) = 1 × 109 m
Mega	M	106	1 megameter (Mm) = 1 × 106 m
Kilo	k	103	1 kilometer (km) = 1 × 103 m
Deci	d	10-1	1 decimeter (dm) = 0.1 m
Centi	c	10-2	1 centimeter (cm) = 0.01 m
Milli	m	10-3	1 millimeter (mm) = 0.001 m
Micro	μ	10-6	1 micrometer (μm) = 1 × 10-6 m
Nano	n	10-9	1 nanometer (nm) = 1 × 10-9 m
Pico	p	10-12	1 picometer (pm) = 1 × 10-12 m
Femto	f	10-15	1 femtometer (fm) = 1 × 10-15 m

Temperature Scales

Celsius, Kelvin, and Fahrenheit

Temperature is a measure of the average kinetic energy of particles. The Celsius and Kelvin scales are most commonly used in science. The Kelvin scale is the SI unit for temperature and is an absolute scale (no negative values).

• Celsius (°C): Water freezes at 0°C and boils at 100°C.

• Kelvin (K): Water freezes at 273 K and boils at 373 K. Conversion: $K = \degree C + 273.15$

• Fahrenheit (°F): Water freezes at 32°F and boils at 212°F.

Volume and Its Measurement

Metric Units of Volume

Volume is the amount of space occupied by a substance. The most common metric units are the liter (L) and milliliter (mL). Relationships include:

• 1 L = 1 dm3

• 1 mL = 1 cm3 = 1 cc

Measuring Volume

Different laboratory glassware is used to measure and deliver specific or variable volumes of liquids. Common devices include graduated cylinders, syringes, burettes, pipettes, and volumetric flasks.

• Graduated cylinder: Used to deliver variable volumes.

• Syringe: Used to deliver variable volumes.

• Burette: Used to deliver a specific volume, with a stopcock to control flow.

• Pipette: Used to deliver a specific volume.

• Volumetric flask: Used to hold a specific volume.

Volume by Displacement

The volume of an irregular object can be determined by the displacement of liquid in a graduated cylinder. The difference in volume before and after the object is submerged equals the object's volume.

Density

Definition and Calculation

Density is a physical property defined as mass per unit volume. It is commonly expressed in g/mL or g/cm3.

• Formula: $d = \frac{m}{V}$

• To solve for mass: $m = d \times V$

• To solve for volume: $V = \frac{m}{d}$

Density can be used to identify substances and to convert between mass and volume.

Uncertainty in Measurement

Exact vs. Inexact Numbers

Exact numbers are known with complete certainty (e.g., 12 eggs in a dozen). Inexact numbers are obtained by measurement and have some degree of uncertainty.

Reporting Uncertainty

All measurements have uncertainty, typically in the last digit. For example, 2.49 mL ± 0.01 mL. The uncertainty should always be indicated.

Accuracy and Precision

Definitions

• Accuracy: How close a measurement is to the true value.

• Precision: How close repeated measurements are to each other.

It is possible to have high precision but low accuracy, and vice versa.

Significant Figures

Rules for Determining Significant Figures

• All nonzero digits are significant.

• Zeroes between significant digits are significant.

• Leading zeroes are not significant.

• Trailing zeroes are significant only if a decimal point is present.

Significant figures reflect the precision of a measurement.

Significant Figures in Calculations

• Addition/Subtraction: The result should have the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: The result should have the same number of significant figures as the measurement with the fewest significant figures.

Scientific Notation

Purpose and Application

Scientific notation expresses very large or small numbers as a product of a number between 1 and 10 and a power of ten. This makes calculations and communication of measurements easier and more precise.

• Example: 3,820 = $3.82 \times 10^3$

• Example: 0.0478 = $4.78 \times 10^{-2}$

Dimensional Analysis

Unit Conversion

Dimensional analysis uses conversion factors to change one unit to another. Conversion factors are derived from equivalence statements (e.g., 1 in = 2.54 cm).

Practice and Applications

Health and Medicine: Dosage Calculations

Dosage calculations use conversion factors from medication labels to ensure correct administration. For example, if a tablet contains 325 mg of active ingredient, this can be used to convert between tablets and milligrams.

Toxicology: LD50

The LD50 (lethal dose, 50%) is a measure of toxicity, indicating the dose required to kill 50% of test subjects. It is usually expressed in mg/kg of body mass. Calculations can determine how much of a substance would reach the LD50 for a given body mass.

Additional info: Mastery of these measurement concepts is essential for success in all areas of chemistry, including laboratory work, data analysis, and safe medication administration.