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

Introduction to Matter, Energy, and Measurement

Overview

This chapter introduces fundamental concepts in chemistry, including the nature of matter and energy, and the importance of measurement in scientific study. Understanding these basics is essential for all subsequent topics in General, Organic, and Biological (GOB) Chemistry.

Units of Measurement

SI Units and Metric System

The metric system is the standard for scientific measurement worldwide. The Système International d’Unités (SI) defines seven base units, each corresponding to a physical quantity. All other units are derived from these base units.

• Base Units: Each physical quantity has a unique base unit.

• Abbreviations: Units are abbreviated for convenience.

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 express multiples or fractions of base units, making measurements more practical for different scales.

• Common Prefixes: Giga (G), Mega (M), Kilo (k), Deci (d), Centi (c), Milli (m), Micro (μ), Nano (n), Pico (p), Femto (f).

• Equivalence Statements: Used for conversions, e.g., 1 km = 1 × 103 m.

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

Temperature Scales

Temperature is a measure of the average kinetic energy of particles. The Celsius and Kelvin scales are most commonly used in scientific measurements.

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

• Kelvin (K): Absolute zero is 0 K; water freezes at 273 K and boils at 373 K.

• Fahrenheit (°F): Used in some countries; water freezes at 32°F and boils at 212°F.

Temperature Conversions

• Kelvin to Celsius: $K = \text{°C} + 273.15$

• Celsius to Kelvin: $\text{°C} = K - 273.15$

Changes in temperature (ΔT) are the same in both Celsius and Kelvin scales.

Volume

Volume Units and Equivalences

Volume is commonly measured in liters (L) and milliliters (mL). The relationships between cubic measurements and volume units are important for laboratory work.

• 1 L = 1 dm3

• 1 mL = 1 cm3 = 1 cc

Measuring Volume

Different laboratory glassware is used to measure and deliver volumes of liquids. Some are designed for variable volumes, others for specific volumes.

• Graduated cylinder: Used for variable volumes.

• Syringe: Used for variable volumes.

• Burette: Used for variable volumes, with a stopcock to control flow.

• Pipette: Used to deliver a specific volume.

• Volumetric flask: Used to hold a specific volume.

Volume by Displacement

Volume can be measured by displacement, especially for irregularly shaped objects. The object is submerged in a liquid, and the change in liquid level indicates the volume.

Density

Definition and Calculation

Density is a physical property defined as mass divided by volume. It is commonly expressed in grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3).

• Formula: $d = \frac{m}{V}$

• Solving for mass: $m = d \times V$

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

Example: 1 kg of iron occupies less volume than 1 kg of air, so iron has a higher density.

Uncertainty in Measurement

Exact vs. Inexact Numbers

Exact numbers are defined by standards (e.g., 12 eggs in a dozen), while inexact numbers are obtained by measurement and have some uncertainty.

Reporting Uncertainty

All measurements have some degree of uncertainty, typically in the last digit reported. For example, 27 °C ± 1 °C.

Accuracy and Precision

Definitions

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

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

Data sets can be classified as having good or poor accuracy and precision.

Significant Figures

Rules for Determining Significant Figures

• All nonzero digits are significant.

• Zeroes between significant digits are significant.

• Zeroes at the beginning are not significant.

• Zeroes at the end are significant if a decimal point is present.

Examples: 3.25 (3 s.f.), 0.0057 (2 s.f.), 8000. (4 s.f.)

Significant Figures in Calculations

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

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

Do not round early in multi-step calculations; apply significant figure rules at the end.

Scientific Notation

Usage and Application

Scientific notation is used to express very large or very small numbers. The significant digits are written as a number between 1 and 10, followed by a power of ten.

• Example: 3820 = 3.82 × 103

• Example: 0.0478 = 4.78 × 10-2

Dimensional Analysis

Conversion Factors

Dimensional analysis is used to convert one quantity to another using conversion factors based on equivalence statements.

• Example: 1 in = 2.54 cm

• Conversion factors: $\frac{1\ \text{in}}{2.54\ \text{cm}}$ or $\frac{2.54\ \text{cm}}{1\ \text{in}}$

Health & Medicine Applications

Dosage Calculations

Dosage is often calculated using conversion factors from medication labels. For example, 325 mg per tablet of aspirin.

• Example: If a patient needs 1.25 g of amoxicillin and each tablet contains 250 mg, the number of tablets required is $\frac{1.25\ \text{g}}{250\ \text{mg}}$ (convert grams to milligrams first).

Toxicology

LD50 and Risk Assessment

The LD50 (lethal dose for 50% of test animals) is a standard measure of toxicity. Dosage is typically measured in mg/kg or μg/kg of body mass.

• Example: The LD50 of caffeine is 192 mg/kg. For a 59 kg person, the lethal dose is $192 \times 59 = 11328$ mg, or 113 cups of coffee (100 mg/cup).

Additional info: These notes cover all major concepts from Chapter 1, including measurement, units, conversions, accuracy, precision, significant figures, scientific notation, and applications in health and toxicology. All images included are directly relevant to the explanations provided.