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

Introduction to Chemistry: Matter, Energy, and Measurement

Chemistry is the study of matter, its properties, and the changes it undergoes. Accurate measurement and understanding of units are foundational to all chemical sciences. This chapter introduces the metric and SI systems, measurement techniques, and the importance of precision and accuracy in scientific work.

Units of Measurement

SI Base Units

The International System of Units (SI) is the standard system used in science. It consists of seven base units, each corresponding to a fundamental physical quantity.

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 convenient.

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.

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

Conversion formulas:

• $K = ^\circ C + 273.15$

• $^\circ C = K - 273.15$

Volume and Its Measurement

Metric Units of Volume

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

• 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

Volume can be measured by the displacement of liquid when an object is submerged. The change in liquid level equals the object's volume.

Density

Definition and Calculation

Density is a physical property defined as mass per unit volume:

• $d = \frac{m}{V}$

Units commonly used: g/mL or g/cm3. Rearranged equations:

• $m = d \times V$

• $V = \frac{m}{d}$

Density helps distinguish substances and is used in calculations involving 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 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.

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 if a decimal point is present.

Significant figures are important for reporting the correct precision in calculated results.

Significant Figures in Calculations

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

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

Scientific Notation

Scientific notation expresses numbers as a product of a number between 1 and 10 and a power of ten. This is useful for very large or small numbers.

• Example: 3820 = $3.82 \times 10^3$

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

Dimensional Analysis

Conversion Factors

Dimensional analysis uses conversion factors to convert between units. Each equivalence statement provides two conversion factors (reciprocals).

• Example: 1 in = 2.54 cm gives $\frac{1\ in}{2.54\ cm}$ and $\frac{2.54\ cm}{1\ in}$

Health & Medicine Applications

Dosage Calculations

Dosage is often calculated using conversion factors from medication labels. For example, if a tablet contains 325 mg of active ingredient, the conversion factor is $\frac{325\ mg}{1\ tablet}$.

Toxicology

LD50 and Risk Assessment

The LD50 (lethal dose, 50%) is the amount of a substance that causes death in 50% of test animals, usually expressed in mg/kg. This value helps assess the toxicity of substances.

Additional info: This chapter provides foundational skills for all subsequent topics in chemistry, including measurement, calculation, and laboratory technique.