General Chemistry Study Notes: Matter, Measurement & Problem Solving

Chapter 1: Matter, Measurement & Problem Solving

Classification of Matter

Matter is anything that occupies space and has mass. Understanding how matter is classified is fundamental in chemistry, as it helps distinguish between different types of substances and mixtures.

• Pure Substance: Matter with a fixed composition; can be an element or a compound.

• Mixture: Matter composed of two or more substances physically combined; can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

Type	Definition	Example
Element	Cannot be broken down into simpler substances	Gold (Au)
Compound	Composed of two or more elements chemically bonded	Water (H2O)
Homogeneous Mixture	Uniform composition throughout	Salt water
Heterogeneous Mixture	Non-uniform composition	Sand and iron filings

Example: Crystalline sugar is a pure substance; salsa is a heterogeneous mixture.

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical. Physical changes do not alter the chemical composition, while chemical changes result in new substances.

• Physical Change: Change in state or appearance without changing composition (e.g., melting, dissolving).

• Chemical Change: Change that alters the chemical composition, forming new substances (e.g., burning, rusting).

Type of Change	Example
Physical	Dissolving sugar in water
Chemical	Cooking an egg

Reversible and Irreversible Changes

Physical and chemical changes can be reversible or irreversible. Reversible changes can be undone, while irreversible changes cannot restore the original substance.

• Reversible Change: Phase changes (e.g., melting, freezing).

• Irreversible Change: Chemical reactions (e.g., combustion).

Example: Dissolving sugar in water is reversible; burning wood is irreversible.

Chemical Properties

Chemical properties describe how a substance reacts with other substances, resulting in a change in composition.

• Examples: Reactivity with acids, flammability, oxidation.

Example: Hydrogen gas reacts explosively with oxygen gas.

Physical Properties

Physical properties can be observed or measured without changing the substance's chemical identity.

• Examples: Color, melting point, density, state of matter.

Example: Mercury is a silvery liquid at 25°C.

Intensive vs. Extensive Properties

Properties of matter are classified as intensive or extensive based on their dependence on the amount of substance.

• Intensive Properties: Independent of the amount (e.g., density, melting point).

• Extensive Properties: Dependent on the amount (e.g., mass, volume).

Property Type	Examples
Intensive	Density, temperature, boiling point
Extensive	Mass, volume, energy

SI Units and Measurements

The International System of Units (SI) provides standard units for scientific measurements. Understanding base units and derived units is essential for accurate data collection and analysis.

Physical Quantity	Name	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Amount of substance	mole	mol

Perimeter, Area, and Volume:

• Perimeter: $P = 2l + 2w$

• Area: $A = l \times w$

• Volume (rectangular): $V = l \times w \times h$

Metric Prefixes

Metric prefixes are used to express multiples or fractions of base units, making it easier to handle very large or small measurements.

Prefix	Symbol	Multiplier
kilo	k	$10^3$
centi	c	$10^{-2}$
milli	m	$10^{-3}$
micro	μ	$10^{-6}$

Example: Convert 654 kg to g: $654 \text{ kg} \times 1000 = 654,000 \text{ g}$

Temperature and Temperature Conversion

Temperature measures the average kinetic energy of particles. Common units are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

• Conversion formulas:

$K = ^\circ C + 273.15$ $^\circ F = \frac{9}{5}(^\circ C) + 32$

Scientific Notation

Scientific notation is used to express very large or small numbers in a compact form.

• Format: $a \times 10^n$ where $1 \leq a < 10$ and $n$ is an integer.

• Example: $6,800,000 = 6.8 \times 10^6$

Significant Figures

Significant figures indicate the precision of a measurement. The rules for counting significant figures depend on the type of number (measured, counted, or defined).

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros are significant only if there is a decimal point.

Example: 0.00364 has 3 significant figures.

Precision in Measurements

Precision refers to how close repeated measurements are to each other. When recording measurements, always estimate one digit beyond the smallest scale division.

Significant Figures in Calculations

When performing calculations, the number of significant figures in the result depends on the operation:

• Multiplication/Division: Result has the same number of significant figures as the value with the fewest significant figures.

• Addition/Subtraction: Result has the same number of decimal places as the value with the fewest decimal places.

Conversion Factors

Conversion factors are ratios used to express a quantity in different units. They are essential for solving problems involving unit conversions.

• Example: 1 hour = 60 minutes

• Common conversion factors: length (1 in = 2.54 cm), mass (1 kg = 1000 g), volume (1 L = 1000 mL)

Dimensional Analysis

Dimensional analysis is a systematic method for converting between units using conversion factors. It involves multiplying by ratios that cancel unwanted units and introduce desired units.

• General format: $\text{Given amount} \times \frac{\text{Conversion factor}}{\text{Unit to cancel}} = \text{End amount}$

Density

Density is a physical property defined as mass per unit volume. It is used to identify substances and solve problems involving mass and volume.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: g/cm3 for solids and liquids, g/L for gases

Example: If a metal has a mass of 21.4 g and a volume of 10.0 cm3, its density is $2.14 \text{ g/cm}^3$.

Density of Geometric and Non-Geometric Objects

For regular shapes, use geometric formulas to find volume. For irregular shapes, use water displacement.

• Geometric objects: $V_{cube} = a^3$, $V_{sphere} = \frac{4}{3}\pi r^3$

• Water displacement: Volume change in graduated cylinder equals volume of object.

Example: If water rises from 200 mL to 265 mL after adding a solid, the object's volume is 65 mL.

Additional info: These notes cover all major introductory concepts in Chapter 1 of General Chemistry, including classification of matter, physical and chemical changes, properties, measurement, SI units, scientific notation, significant figures, conversion factors, dimensional analysis, and density. Practice questions and examples are included to reinforce understanding.