Ch.1 - Introduction: Matter & Measurement

Classification of Matter

Matter is anything that occupies space and has mass. Understanding how matter is classified is foundational to chemistry.

• Pure Substances: Matter with a fixed composition and distinct properties. Examples include elements (e.g., gold, oxygen) and compounds (e.g., water, sodium chloride).

• Mixtures: Physical combinations of two or more substances where each retains its own identity and properties. Mixtures can be homogeneous (uniform composition, e.g., saltwater) or heterogeneous (non-uniform composition, e.g., salad).

Example: Classify the following: Gatorade (homogeneous mixture), Crystalline sugar (pure substance), Lead wire (element), Salsa (heterogeneous mixture).

Physical and Chemical Changes

Changes in matter are categorized as physical or chemical based on whether the composition of the substance changes.

• Physical Changes: Alter the form or appearance of matter but do not change its composition. Examples: melting ice, dissolving sugar in water.

• Chemical Changes: Result in the formation of one or more new substances with different properties. Examples: burning wood, rusting iron.

Example: Dissolving sugar in water is a physical change; burning wood is a chemical change.

Reversible and Irreversible Changes

Physical changes can be reversible (e.g., melting/freezing) or irreversible (e.g., cutting paper). Chemical changes are generally irreversible under normal conditions.

• Reversible: Melting and freezing water.

• Irreversible: Cooking an egg, burning paper.

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes, forming new substances.

• Examples: Reactivity with acids, flammability, oxidation states.

Example: High reactivity with acids is a chemical property; having a yellow-orange color is not.

Physical Properties

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

• Examples: Color, melting point, density, boiling point, state of matter at room temperature.

Example: Mercury is a silvery liquid at 25°C (physical property).

Intensive vs. Extensive Properties

Properties of matter are classified based on their dependence on the amount of substance present.

• Intensive Properties: Do not depend on the amount of matter (e.g., density, melting point, temperature).

• Extensive Properties: Depend on the amount of matter (e.g., mass, volume, energy).

SI Units and Measurements

The International System of Units (SI) is the standard for scientific measurements. Each physical quantity has a base unit.

Area is measured in , volume in .

Metric Prefixes

Metric prefixes indicate multiples or fractions of base units.

Example: To convert 654 kg to g, multiply by (1 kg = 1000 g).

Temperature and Its Measurement

Temperature is a measure of the average kinetic energy of particles in a substance. Common units are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

• Kelvin to Celsius:

• Celsius to Fahrenheit:

Scientific Notation

Scientific notation expresses very large or small numbers in the form , where and is an integer.

• Example:

• To convert to scientific notation, move the decimal point to create a number between 1 and 10, adjusting the exponent accordingly.

Significant Figures

Significant figures (sig figs) are the digits in a measurement that are known with certainty plus one estimated digit.

• Rules for counting sig figs:

  • 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.

• When multiplying/dividing, the result should have as many sig figs as the value with the fewest sig figs.

• When adding/subtracting, the result should have as many decimal places as the value with the fewest decimal places.

Conversion Factors and Dimensional Analysis

Conversion factors are ratios used to express a quantity in different units. Dimensional analysis is a systematic approach to problem-solving that uses conversion factors to move from one unit to another.

• Example: To convert 2 hours to minutes:

Density

Density is the amount of mass per unit volume of a substance.

• Formula:

• Units: for solids and liquids, for gases.

Example: If a metal has a mass of 21.4 g and a volume of 2.0 cm3, its density is .

Density of Geometric and Non-Geometric Objects

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

• Volume of a cube: (where is the length of a side)

• Water displacement: Volume of object = Final water level - Initial water level

Example: If a solid raises the water level from 200 mL to 265 mL, its volume is 65 mL.

Summary Table: Key Concepts

Additional info: Practice problems and examples are included throughout to reinforce concepts and provide application opportunities. These notes are structured to cover all foundational aspects of matter and measurement as outlined in a typical General Chemistry curriculum.